Patent Publication Number: US-2015081746-A1

Title: System, A Data Structure for Controlling the System, and A Method for Updating the Data Structure

Description:
BACKGROUND 
     Electronic devices, e.g. smart phones and computers, may carry a plurality of functionalities, for example programs for different needs and modules for positioning, communication and entertainment. The variety of tasks that can be performed with these devices is large, and the individual tasks may be complex in nature. A lot of the work carried out in today&#39;s world is done with the help of computers. Electronic devices have become a part of everyday life in free time, as well. 
     The user of the electronic device may be overwhelmed by the variety of functions provided by the device. For this purpose, the devices may provide ways of customizing the looks and the arrangement of functions in the device so that the functions needed by the user are easily reachable. 
     The user may customize the device e.g. by using a user interface. 
     SUMMARY 
     An object of the invention is to provide a method for updating a data structure. An object of the invention is to provide a computer program for updating a data structure. An object of the invention is to provide a computer program product for updating a data structure. An object of the invention is to provide an apparatus for updating and storing co-occurrence data. An object of the invention is to provide a system for updating and storing co-occurrence data. An object of the invention is to provide means for storing co-occurrence data. An object of the invention is to provide a data structure containing co-occurrence data. 
     According to a first aspect of the invention, there is provided a method, comprising:
         determining a first word (W 1 ) based on a state of a system ( 500 ) and/or based on a physical quantity detected by a sensor (G 1 ),   forming a first word group (BAG1) comprising the first word (W 1 ) and a second word (W 2 ),   associating the first word (W 1 ) with a first sparse vector (a 1 ) or with a common sparse vector (b 1 ),   associating the second word (W2) with a second sparse vector (a 2 ) or with the common sparse vector (b 1 ),   associating the first word (W 1 ) with a first vector (v 1 ) of a matrix (EX 1 ),   associating the second word (W 2 ) with a second vector (v 2 ) of the matrix (EX 1 ),   modifying the first vector (v 1 ) of the matrix (EX 1 ) by adding contribution of the second sparse vector (a 2 ) or the contribution of the common sparse vector (b 1 ) to the first vector of the matrix (EX 1 ), and   modifying the second vector (v 2 ) of the matrix (EX 1 ) by adding contribution of the first sparse vector (a 1 ) or the contribution of the common sparse vector (b 1 ) to the second vector of the matrix (EX 1 ).       

     According to a second aspect of the invention, there is provided a computer program (PROG1), which when executed by one or more data processors (CNT1) is for performing a method comprising:
         determining a first word (W 1 ) based on a state of a system ( 500 ) and/or based on a physical quantity detected by a sensor (G 1 ),   forming a first word group (BAG1) comprising the first word (W 1 ) and a second word (W 2 ),   associating the first word (W 1 ) with a first sparse vector (a 1 ) or with a common sparse vector (b 1 ),   associating the second word (W2) with a second sparse vector (a 2 ) or with the common sparse vector (b 1 ),   associating the first word (W 1 ) with a first vector (v 1 ) of a matrix (EX 1 ),   associating the second word (W 2 ) with a second vector (v 2 ) of the matrix (EX 1 ),   modifying the first vector (v 1 ) of the matrix (EX 1 ) by adding contribution of the second sparse vector (a 2 ) or the contribution of the common sparse vector (b 1 ) to the first vector of the matrix (EX 1 ), and   modifying the second vector (v 2 ) of the matrix (EX 1 ) by adding contribution of the first sparse vector (a 1 ) or the contribution of the common sparse vector (b 1 ) to the second vector of the matrix (EX 1 ).       

     According to a third aspect of the invention, there is provided a computer-readable medium (MEM5) storing computer code (PROG1), which when executed by one or more data processors (CNT1) is for performing a method comprising:
         determining a first word (W 1 ) based on a state of a system ( 500 ) and/or based on a physical quantity detected by a sensor (G 1 ),   forming a first word group (BAG1) comprising the first word (W 1 ) and a second word (W 2 ),   associating the first word (W 1 ) with a first sparse vector (a 1 ) or with a common sparse vector (b 1 ),   associating the second word (W2) with a second sparse vector (a 2 ) or with the common sparse vector (b 1 ),   associating the first word (W 1 ) with a first vector (v 1 ) of a matrix (EX 1 ),   associating the second word (W 2 ) with a second vector (v 2 ) of the matrix (EX 1 ),   modifying the first vector (v 1 ) of the matrix (EX 1 ) by adding contribution of the second sparse vector (a 2 ) or the contribution of the common sparse vector (b 1 ) to the first vector of the matrix (EX 1 ), and   modifying the second vector (v 2 ) of the matrix (EX 1 ) by adding contribution of the first sparse vector (a 1 ) or the contribution of the common sparse vector (b 1 ) to the second vector of the matrix (EX 1 ).       

     According to a fourth aspect of the invention, there is provided an apparatus ( 400 ,  500 ,  1251 ), comprising:
         a first memory (MEM1) for storing words (W 1 ,W 2 ) of a group (BAG1),   a sparse vector supply (SUP1) for providing sparse vectors (a 1 , a 2 , b 1 ),   a second memory (MEM2) for storing vectors of a matrix (EX 1 ), and   a combining unit (LCU1) for modifying vectors of the matrix (EX 1 ) by adding contributions of sparse vectors (a 1 , a 2 , b 1 ) associated with the words (W 1 ,W 2 ).       

     According to a fifth aspect of the invention, there is provided a system ( 400 ,  500 ), comprising:
         a first memory (MEM1) for storing words (W 1 ,W 2 ) of a group (BAG1),   a sparse vector supply (SUP1) for providing sparse vectors (a 1 , a 2 , b 1 ),   a second memory (MEM2) for storing vectors of a matrix (EX 1 ), and   a combining unit (LCU1) for modifying vectors of the matrix (EX 1 ) by adding contributions of sparse vectors (a 1 , a 2 , b 1 ) associated with the words (W 1 ,W 2 ).       

     According to a sixth aspect of the invention, there is provided a means ( 400 , 500 ) for storing co-occurrence data, said means comprising:
         a first means (MEM1) for storing data configured to store words (W 1 ,W 2 ) of a group (BAG1),   a means (SUP1) for supplying sparse vectors configured to provide sparse vectors (a 1 , a 2 , b 1 ),   a second means (MEM2) for storing data configured to store vectors of a matrix (EX 1 ), and   a means (LCU1) for combining configured to modify vectors of the matrix (EX 1 ) by adding contributions of sparse vectors (a 1 , a 2 , b 1 ) associated with the words (W 1 ,W 2 ).       

     According to a seventh aspect of the invention, there is provided a data structure (EX 1 ) for controlling the operation of a computer system, said data structure (EX 1 ) comprising co-occurrence data stored as sparse high-dimensional vectors associated with words of a vocabulary (VOC1), said vectors being associated with at least three types of words from the group of time descriptor words, location descriptor words, internet address words, operating state descriptor words, brand names, user phonebook names and sensor value words. 
     According to an eighth aspect of the invention, there is provided a computer program product embodied on a non-transitory computer-readable medium, said medium including one or more computer-executable instructions that when executed by one or more processors cause a system to carry out the following:
         to determine a first word based on a state of a system and/or based on a physical quantity detected by a sensor,   to form a first word group comprising the first word and a second word,   to associate the first word with a first sparse vector or with a common sparse vector,   to associate the second word with a second sparse vector or with the common sparse vector,   to associate the first word with a first vector of a matrix,   to associating the second word with a second vector of the matrix,   to modify the first vector of the matrix by adding contribution of the second sparse vector or the contribution of the common sparse vector (b 1 ) to the first vector of the matrix, and   to modify the second vector of the matrix by adding contribution of the first sparse vector or the contribution of the common sparse vector to the second vector of the matrix.       

     According to a further embodiment of the invention, the apparatus ( 400 ,  500 ,  1251 ) may comprise:
         a first memory (MEM1) for storing words (W 1 ,W 2 ) of a group (BAG1),   a sparse vector supply (SUP1) for providing sparse vectors (a 1 , a 2 , b 1 ),   a second memory (MEM2) for storing vectors of a matrix (EX 1 ), and   a combining unit (LCU1) for modifying vectors of the matrix (EX 1 ) by adding contributions of sparse vectors (a 1 , a 2 , b 1 ) associated with the words (W 1 ,W 2 ).       

     According to a further embodiment of the invention, the combining unit (LCU1) may be arranged to modify the first vector (v 1 ) by forming a linear combination of the first vector of the matrix (EX 1 ) and one or more sparse vectors (a 2 , b 1 ). 
     According to a further embodiment of the invention, the number of non-zero elements of the first sparse vector is in the range of 4 to 1000, and wherein the number of non-zero elements of the first sparse vector is also in the range of 0.1% to 10% of the length of the first sparse vector. 
     According to a further embodiment of the invention, the apparatus may comprise an interface ( 501 ) to receive a word (W 3 ) for said bag (BAG1). 
     According to a further embodiment of the invention, the apparatus may be configured to operate such that the first word (W 1 ) represents a state at a first time (t 1 ), and the second word (W 2 ) represents a state at a second different time (t 2 ). 
     According to a further embodiment of the invention, the apparatus may comprise a memory (MEM3) for storing a vocabulary (VOC1), wherein a sparse vector supply (SUP1) and/or a combining unit (LCU1) and/or a control unit (CNT1) is configured to associate words (W1, W2) with the sparse vectors (a 1 ,a 2 ) by using the vocabulary (VOC1). 
     According to a further embodiment of the invention, the sparse vector supply (SUP1) and/or the combining unit (LCU1) and/or the control unit (CNT1) is configured to ignore a word, which is not contained in the vocabulary (VOC1). 
     According to a further embodiment of the invention, the sparse vector supply (SUP1) and/or the combining unit (LCU1) and/or the control unit (CNT1) may be configured to add a further word to the vocabulary (VOC1) when the further word is a system word, a uniform resource locator (URL), or a word classified to be a vocabulary word. 
     According to a further embodiment of the invention, the combining unit (LCU1) and/or the control unit (CNT1) may be configured to store the values of the matrix by using hash tables (VOC1, IND, CAH1, OCCL) such that a vector (v 1 ) of the matrix (EX 1 ) has a non-zero element (e ik ) at a column (i) of the matrix (EX 1 ), and a hash table (OCCL i ) contains a pointer identifying a word (w k ) of a vocabulary (VOC1) associated with the vector (v k ). 
     According to a further embodiment of the invention, a control unit (CNT1) may be configured to determine an auxiliary word (T6) from a first word (W 1 ,T1) by using a calendar, dictionary, electronic map, and/or tokenizing. 
     According to a further embodiment of the invention, the apparatus may comprise an interface for copying vectors (v 1 ,v 2 ) of the matrix (EX 1 ) from a device ( 1240 ) to a memory (MEM2) of said apparatus. 
     According to a further embodiment of the invention, the apparatus may comprise one or more sensors (NAV1, G 1 ) arranged to provide one or more words based on a detected environmental condition. 
     The state of a system as well as the situation where the system is used may have an effect on the preferences and the needs of a user. 
     According to an embodiment of the invention, co-occurrence data representing preferences and facts observed in a plurality of situations may be stored in a matrix as combinations of high-dimensional sparse vectors. The matrix may be called e.g. as an experience matrix or a context matrix. The data stored in the experience matrix may be subsequently utilized e.g. for predicting a preference of a user in a new situation. 
     The system may be capable of carrying out various tasks by running one or more applications (i.e. by executing program code) and/or by activating one or more functional (physical) units. The tasks may include e.g. receiving and sending messages, playing music, updating a calendar, browsing in the internet, and/or navigating in the streets of a city. The system may comprise e.g. a camera for capturing images and/or a satellite navigation unit for determining location. 
     The user of the system may activate one or more applications and/or functional units by using a user interface. However, sometimes a high number of consecutive input commands may be needed to navigate in the menu structures of the system, in order to activate the functionalities needed in a given situation. Making of selections in complex menu structures may be time-consuming. The user may also have difficulties in memorizing where a relevant menu resides in the menu structure of the system. 
     Activated applications and units may consume system resources. Applications and units which are not needed may be stopped in order to allocate more resources to applications which are necessary or at least useful in the given situation. Stopping of an application or unit may require navigating in the menu structures of the system, again. 
     In an embodiment, selecting applications and units to be activated in a situation may be facilitated by automatically presenting a menu with a limited set of options. A menu of the system may be presented to a user based on a prediction determined by utilizing co-occurrence data stored in the experience matrix. 
     In an embodiment, activation and/or stopping of a functionality may be controlled based on a prediction determined by using co-occurrence data stored as vectors in an experience matrix EX 1 . The system may automatically activate and/or deactivate a functionality, based on one or more query words derived from present conditions, past conditions and/or future conditions. Thus, the user needs to pay less attention to giving commands to the system. In an embodiment, a user may have previously authorized the system to automatically activate and/or deactivate a functionality without specifically asking permission from the user. 
     Using data stored in the experience matrix may be used e.g. when handling high amounts of co-occurrence data, because human interaction is not necessary to interpret the data. 
     In an embodiment, semantic information may be extracted automatically, in an unsupervised fashion from unstructured data. Little or no preprocessing of data may be needed. Little or no human interaction may be needed. In an embodiment, no prior knowledge of the meaning words need to be assumed, making the method easy to apply to data with different topical and structural properties. 
     In an embodiment, the system does not need to store data specifying the semantic meaning of the words. The system may store the data and be controlled by the data even without knowledge about the semantic meaning of the words. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following examples, various embodiments of the invention will be described in more detail with reference to the appended drawings of example embodiments, in which 
         FIG. 1   a  shows, by way of example, representing words as basic sparse vectors, 
         FIG. 1   b  shows, by way of example, bags of words, 
         FIG. 1   c  shows, by way of example, an experience matrix after updating with the bags of  FIG. 1   b,    
         FIG. 2  shows, by way of example, updating an experience matrix by using a bag of words and the basic sparse vectors of  FIG. 1   a,    
         FIG. 3   a  shows, by way of example, providing a prediction by using an experience matrix, 
         FIG. 3   b  illustrates, by way of example, determining a difference of vectors in a context space, 
         FIG. 3   c  shows, by way of example, providing a prediction by using an experience matrix, 
         FIG. 4   a  shows, by way of example, representing bags of words as basic sparse vectors, 
         FIG. 4   b  shows, by way of example, updating an experience matrix by using a bag of words and the basic sparse vectors of  FIG. 4   a,    
         FIG. 4   c  shows, by way of example, an experience matrix after updating with the bags of  FIG. 4   a,    
         FIG. 5   a  shows, by way of example, collecting words to a bag, 
         FIG. 5   b  shows, by way of example, collecting words to a bag, the words representing different instants of time, 
         FIG. 5   b  shows, by way of example, collecting words to a bag, the words representing different instants of time, 
         FIG. 6  illustrates, by way of example, gathering and processing data in a system comprising an experience matrix, 
         FIG. 7   a  shows, by way of example, a system configured to gather and process data by using an experience matrix, 
         FIG. 7   b  shows, by way of example, a sensor arranged to provide words as the output, 
         FIG. 7   c  shows, by way of example, a sparse vector supply comprising a word hash table and a group of basic sparse vectors, 
         FIG. 7   d  shows, by way of example, a sparse vector supply comprising a group of basic sparse vectors, 
         FIG. 7   e  shows, by way of example, a sparse vector supply comprising a random number generator configured to generate basic sparse vectors, 
         FIG. 7   f  shows, by way of example, a system, which is controlled based on a prediction made by using an experience matrix, 
         FIG. 8   a  shows, by way of example, bags of words, 
         FIG. 8   b  shows, by way of example, a user interface controlled based on a prediction, 
         FIG. 8   c  shows, by way of example, a user interface controlled based on a prediction, 
         FIG. 8   d  shows, by way of example, method steps for preparing the system for a calendar event, 
         FIG. 9   a  shows, by way of example, representing an experience matrix as a group of hash tables, 
         FIG. 9   b  shows, by way of example, updating the experience matrix of  FIG. 9   a,    
         FIG. 9   c  shows, by way of example, using the experience matrix of  FIG. 9   a  for making a prediction, 
         FIG. 10   a  shows, by way of example, generating auxiliary words by using a calendar and/or by using a dictionary, 
         FIG. 10   b  shows, by way of example, replacing a word with a second word by using a dictionary, 
         FIG. 11  shows, by way of example, a system comprising an experience matrix, 
         FIG. 12   a  shows, by way of example, a device having a user interface, and 
         FIG. 12   b  shows, by way of example, a data processing device. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     In the following, several example embodiments of the invention will be described with reference to context of a system as well as a framework of random indexing. It is to be noted, however, that the invention is not limited to these uses or alternatives. In fact, the embodiments may also be used in any environment where semantic processing and adaptation of the system is required. 
     Co-occurrence data may be gathered into the experience matrix based on co-occurrences of words in previous situations. The experience matrix may contain historical data about co-occurrences of words in different situations. The experience matrix EX 1  may contain a plurality of sparse vectors, which in turn contain information about historical co-occurrences of words related to a system. The experience matrix EX 1  may contain the “experience” gathered by one or more systems. The experience matrix may be used e.g. to “predict” suitable actions or operating modes which might be applicable in given situation when one or more (other) words related to the situation are known. Thus, the system may change its operation based on observed facts, by using previous experience stored in the experience matrix of the system. 
     In an embodiment, one or more prediction words may be determined from one or more query words, by using the data stored in the experience matrix. The system may be subsequently controlled at least partly based on the prediction words. The query words may be words, which describe the current situation. The prediction words may be words, which are likely to describe the current situation. Co-occurrence data may be stored as vectors of an experience matrix EX 1 . The stored co-occurrence data may be subsequently used for making a prediction. A vocabulary VOC1 may be needed to store co-occurrence data in the experience matrix EX 1  and to utilize co-occurrence data stored in the experience matrix EX 1 . In an embodiment, the vocabulary VOC1 may be used also in connection with another matrix, called the basic matrix RM1. 
     Referring to  FIG. 1   a , a vocabulary VOC1 may comprise a group of different words w 1 , w 2 , . . . w n . The vocabulary VOC1 may be a hash table, which contains pointers to sparse vectors of a basic matrix RM1. The sparse vectors may also be called as random index vectors (RI vectors). Thus, each word w 1 , w 2 , . . . w n  of the vocabulary VOC1 may be associated with a basic sparse vector a 1 , a 2 , . . . a n . For example, a word w k  (e.g. “meeting”) may be associated with a basic sparse vector a k . The basic sparse vectors a 1 , a 2 , . . . a k , . . . a n  may be stored e.g. as rows of the basic matrix RM1. 
     The vocabulary VOC1 may be a hash table, which indicates the location (e.g. row k) of the sparse vector in the basic sparse matrix RM1, by using the word (e.g. w k ) as the key. 
     Each basic sparse vector of the matrix RM1 may represent a word. For example, the basic vector a k  may be interpreted to represent the word w k  in sparse vector format. 
     Each basic sparse vector a k  consists of elements R 1,k , R 2,k , . . . , R ik , . . . R m,k . In an embodiment, the basic sparse vectors a 1 , a 2 , . . . a k , . . . a n  of the matrix RM1 may be unique and different. Each row of the basic matrix RM1 may be a unique basic sparse vector associated with a different word. 
     Each basic sparse vector a k  may have a high number of zero elements and only a few non-zero elements. For example, a basic sparse vector a k  may have e.g. 10000 elements R wherein twenty elements may be non-zero and 9980 elements may be zero. 
     In an embodiment, the sum of all elements of the basic sparse vector a k  may be equal to zero. This may minimize memory consumption, may simplify mathematical operations and/or may increase data processing speed. In particular, 50% of the non-zero elements may be equal to −1 (minus one), and 50% of the non-zero elements may be equal to 1 (one). In other words, the value of an element may be −1, 0 or 1, and the basic sparse vector a k  may be a ternary vector. 
     Each vector a 1 , a 2 , . . . a k , . . . a n  may represented by a point in a multi-dimensional space. More precisely, each vector a 1 , a 2 , . . . a k , . . . a n  may represented by a different end point in the same multi-dimensional space when the starting point of each vector is located at the same point (e.g. origin). The number m of elements R of the basic sparse vector a k  may be e.g. in the range of 100 to 10 6 . The number m nz  of non-zero elements R of the basic sparse vector a k  may be in the range of 0.1% to 10% of the number m, said number m nz  of non-zero elements also being in the range of 4 to 10 3 . Increasing the total number m and/or the number m nz  of non-zero elements may allow using a larger vocabulary VOC1 and/or may provide more reliable predictions. However, increasing the number m and/or m nz  may also require more memory space and more data processing power. 
     R ik  denotes an element of the basic matrix RM1 belonging to the column and to the k th  row. In an embodiment, the vectors may be ternary and the value of an individual element e ik  may be one of the following −1, 0, or 1. The number of negative non-zero elements R may be equal to the number of positive non-zero elements R, the values of the non-zero elements R being integers. This likely to maximize data processing speed, and to minimize the use of memory. However, this is not necessary. For example, a basic sparse vector a k  may have sixteen elements R having a value −0.5 and four elements R having a value 2. 
     When the vectors a 1 , a 2 , . . . a k , . . . a n  of the matrix RM1 are compared with each other, the positions of the non-zero elements in a basic sparse vector a k  and the values of the non-zero elements of the basic sparse vector a k  may be randomly distributed. The basic sparse vectors may also be called as random index vectors. This randomness may ensure with a high probability that the points representing the basic sparse vector in the multi-dimensional space are not too close to each other. If two points representing two different words would be too close to each other, this might lead to erroneous predictions during subsequent processing. When the positions and the values are randomly distributed, this may also ensure with a high probability that each word of the vocabulary VOC1 is associated with a unique and different basic sparse vector. When the indices are random, it is highly probable that the elementary sparse vectors associated with two different words are orthogonal or nearly orthogonal. Thus, the dot product of said elementary sparse vectors is equal to zero at a high probability. This pseudo-orthogonality of the words may preserve the unique identity of each word even when they are represented by the sparse vectors. This pseudo-orthogonality of the words may preserve the unique identity of each word, event or unique occurrence stored in the experience matrix EX 1  when the words, events and/or occurrences are represented as combinations of the sparse vectors in the experience matrix EX 1 . The words of the vocabulary may be arranged e.g. in alphabetical order. 
       FIG. 1   b  shows several sets of words, which may be called e.g. as “bags”. A bag comprises two or more different words related to each other. The number of words in a bag may be e.g. in the range of 2 to 1000. Each bag could also be called as a “document”. 
     The bags represent co-occurrences of words. The bags may be used to educate a system. Information about co-occurrences of the words may be stored in a matrix EX 1  ( FIGS. 1   c ,  4   b ). 
     The words of a bag may e.g. describe a situation and/or a system used in said situation. In particular, the words may represent observed facts. 
     For example, a first bag BAG1 may comprise the words “work”, “morning” and “mail”. The word “work” may be e.g. determined e.g. based on a marking in the calendar of the system. The word “morning” may be provided e.g. by a clock of the system. The word “mail” may be related to the words “work” and “morning” e.g. because the system has detected that a user has received and/or sent written messages in a situation described by the words “work” and “morning”. 
     A second bag BAG2 may comprise the words “home”, “meal” and “music”. The word “home” may be provided e.g. when a navigation unit of carried by a user indicates that the detected location matches with a location called as “home”. The word “meal” may be provided e.g. because food (e.g. pizza) has just been ordered to the location “home” via a delivery service. The system may be arranged to provide a word “music” e.g. because user has instructed the system to play music. 
     The words home, meal and music may represent e.g. a situation prevailing at a first instant t 1 . The words home, meal and music might be inter-related. If this combination of words has occurred several times in the past, it may e.g. used to evaluate (predict) the likelihood at which the user wishes to listen to music when eating meal at home. For example, a portable device may be arranged to set itself into a music playing mode when it determines that the user is eating meal at home. 
     A third bag BAG3 may comprise the words “work”, “meeting” and “silent”. The words “work” and “meeting” may be e.g. determined e.g. based on markings in the calendar of the system. The system may be arranged to provide a status descriptor “work” e.g. based on information contained in a calendar of the user. The system may determine the word “work” also when the location of a portable device of the user matches with the location of the working place. The word “silent” may be derived e.g. because a user attending a meeting has set the system to a silent mode. In particular, the user may have set a mobile phone to an operating mode where the phone does not generate an audible alarm in case of an incoming telephone call. 
     Now, the words work, meeting and silent may represent a situation prevailing at a second time t 2 . If this combination of words has occurred several times in the past, it may e.g. used to evaluate (predict) the likelihood at which the user wishes to set his portable to the silent mode when attending a meeting at work. For example, the portable device of the user may now be arranged to automatically suggest setting into a silent mode when it determines that the user is attending a meeting. 
     Referring to  FIG. 1   c , data derived from observed co-occurrences of words may be stored as vectors v 1 , v 2 , . . . , v k  . . . v n  of a matrix EX 1 , which may be called e.g. as an “experience matrix”. Each word w 1 , w 2 , . . . w n  of the vocabulary VOC1 may (also) be associated with a sparse vector of the experience matrix EX 1 . The sparse vectors v 1 , v 2 , . . . , v k  . . . v n  may be stored e.g. as rows of the experience matrix EX 1 . 
     The vocabulary VOC1 may be the same (hash table) as in  FIG. 1   a.    
     Each vector of the experience matrix EX 1  may be a linear combination of sparse vectors and an initial vector. 
     In particular, each vector of the experience matrix EX 1  may be a linear combination of the basic sparse vectors of the basic sparse matrix RM1 ( FIG. 1   a ). 
     The number n of elements e ik  of an individual vector v k  may be equal to the number n of elements R of an individual basic sparse vector shown in  FIG. 1   a . The combining of the sparse vectors may be carried out according to the contents of the bags ( FIG. 1   b ). 
     The experience matrix EX 1  may contain co-occurrence data obtained from a plurality of bags BAG1, BAG2. When the co-occurrence data obtained from the bags is stored in the experience matrix EX 1  as linear combinations of the sparse vectors, this may represent storing the co-ocurrence data in a compressed format. 
     In an embodiment, the number n of elements e ik  of an individual vector v k  may be substantially smaller than the number of bags from which the co-occurrence data stored in the matrix EX 1  was obtained. 
     It is not necessary to change the number n of elements e ik  when new data is added from a new bag. This means that the matrix EX 1  may be updated fast and easily by using co-occurrence data obtained from further bags. This also means that the size (i.e. the number of rows and columns) of the matrix EX 1  may remain constant even when the matrix EX 1  is updated by using co-occurrence data obtained from the further bags. 
     However, in an embodiment, it might be impossible to unambiguously determine (by using only the vocabulary VOC1 and the matrices RM1, EX 1 ) which ones of the bags used for updating contained a given word. In this sense, storing co-occurrence data of the bags in the matrix EX 1  may represent a lossy way of storing co-occurrence data. 
     The experience matrix EX 1  may be initially a zero matrix (null matrix) but this is not necessary. The initial values of several vectors of the experience matrix EX 1  may exhibit smooth spatial variation. 
       FIG. 2  illustrates how the experience matrix EX 1  may be updated by using a bag of words. The bag of words may be e.g. the bag BAG1 shown in  FIG. 1   b.    
     The symbols W 1 , W 2 , W 3  (with uppercase letter) denote the words of the bag BAG1. The w 1 , w 2 , . . . w n  (with lowercase letter) denote the words of the vocabulary VOC1. Typically, the first word W 1  of the bag is not the same as the first word w 1  of the vocabulary, but sometimes the word W 1  might perhaps be the same as the word w 1 . 
     A vector of the experience matrix EX 1  may be updated based on words contained in a bag. During the updating, the vector of the experience matrix EX 1  may be called e.g. as a target vector. 
     The updating may comprise modifying the target vector (e.g. v P ) associated with a word (e.g. “mail”) of the bag BAG1. A bag contains two or more words W 1 , W 2 , W 3 , . . . When the words W 1 , W 2 , W 3  belong to the same bag BAG1, this indicates, among other things, that the words W 1  and W 2  belong to the context of the word W 3 . 
     One or more other words belonging to a bag together with a first word may be considered to belong to the context of the first word. A word may represent e.g. a state of a system and/or an external condition. 
     The target vector v P  of the experience matrix EX 1  associated with the word W 3  of the bag BAG1 may be identified by using the vocabulary VOC1. More precisely, the location of the vector v P  (row) of the experience matrix EX 1  associated with the value (=w p , “mail”) of the word W 3  may be determined by using the vocabulary VOC1. 
     The basic sparse vectors (e.g. a k+1  and a n−1 ) representing the other words W 1 , W 2  of the bag BAG1 may also be found by using the vocabulary VOC1. 
     Adding co-occurrence data of a bag BAG1 to the experience matrix EX 1  may comprise replacing the (first) target vector v P  associated with the word W 3  of the bag BAG1 with a modified vector which is a linear combination of the (first) target vector v P  and the basic sparse vectors a k+1 , a n−1  representing the other words W 1 , W 2  of the bag BAG1. 
     In an embodiment, the basic sparse vectors a k+1 , a n−1  may be simply summed to the target vector v P . In other words, the weighting coefficient of each basic sparse vectors a k+1 , a n−1  used in the linear combination may be equal to one. However, the weighting coefficient of a basic sparse vector may also deviate from one in order to emphasize or reduce the contribution of the word represented by said basic vector. The weighting coefficient may be e.g. in the range of 0.1 to 10. 
       FIG. 2  shows a cross drawn over the basic vector a p . When the experience matrix EX 1  is updated by using the representative vectors of the basic matrix RM1, the vectors may be combined such the basic vector a p  representing the word W 3  does not contribute to the modified target vector v P  associated with said word W 3 . A word always co-occurs with itself. Adding the contribution of the word&#39;s own basic vector would is not likely to add meaningful new data to the experience matrix. 
     A second target vector (e.g. v n−1  shown in  FIG. 1   c ) representing a second word (work, W 2 ) of the bag BAG1 may be modified by replacing the second target vector v n−1  with a modified vector which is a linear combination of the second target vector v P  and the basic sparse vectors a k+1 , a P  representing the other words W 1  (morning), W 3  (mail) of the bag BAG1. 
     If the bag contains a third word, a third target vector (e.g. v k+1  shown in  FIG. 1   c ) representing a third word (morning, W 1 ) of the bag BAG1 may be modified by replacing the third target vector v k+1  with a modified vector which is a linear combination of the third target vector v k+1  and the basic sparse vectors a n−1 , a P  representing the other words W 2  (work), W 3  (mail) of the bag BAG1. 
     If the bag contains more than three words, a target vector associated with each additional word may be updated by adding contribution of the other words of the bag, respectively. 
     The matrix may be updated by using words of a second bag, and by using words of any subsequent bags, respectively. 
     The two or more words W 1 , W 2 , W 3 , . . . of a bag BAG1 may be provided by a system (system words) and/or by a client (client words). The system words, may be e.g. words describing time and/or location. The “client” may be e.g. a human user, an application or a network service. The client words may be e.g. words obtained from a human user and/or from a running software application. A word may e.g. describe the state of a system. 
       FIG. 3   a  shows making a prediction by using the experience matrix EX 1 . The experience matrix EX 1  may be e.g. the matrix shown in  FIG. 1   c  or  4   b.    
     One or more words representing a state of the system may be predicted by using the experience matrix EX 1 . The prediction method may comprise receiving one or more query words Q 1 , Q 2 , . . . ( FIG. 3   c  shows making a prediction by using two query words). The query words Q 1 , Q 2  may be provided e.g. by the system and/or by a client. In an embodiment, a client may initiate the prediction process by sending one or more query words Q 1 , Q 2 . A vector v k  of the experience matrix EX 1  associated with the query word Q 1  (e.g. morning) may be found by using the vocabulary VOC1. In case of a single query word Q 1 , the associated vector v k  may be used as a query vector QV1 representing the query. 
     The query vector QV1 may now be compared with the vectors v 1 , v 2 , . . . v n  of the experience matrix EX 1  in order to identify one or more vectors v 1 , v 2 , . . . v n  of the experience matrix EX 1  which are substantially similar to the query vector QV1. During the comparing, the vectors v 1 , v 2 , . . . v n  of the experience matrix EX 1  may be called as candidate vectors. The word or words associated with vectors having the smallest difference to the query vector QV1 may be determined and provided as the prediction output OUT1. The prediction method may comprise determining a difference between the query vector QV1 and each vector v 1 , v 2 , . . . v n  of the experience matrix EX 1 . 
       FIG. 3   b  illustrates the query vector QV1 and a few vectors of the experience matrix EX 1  in the multidimensional space when the starting points of the vectors coincide (e.g. at the origin ORIG1). DIM and DIM′ denote two dimensions of the multidimensional space (as discussed above, the number of dimensions of the space may be e.g. 10 4  or higher). If two vectors have at least approximately the same length and at least approximately the same direction in the multidimensional space, this may be interpreted to indicate that said two vectors are associated with two words appearing in substantially similar context. If one of said words is a valid descriptor for a state of the system, it is likely that also the other word is a valid descriptor for a state of the system. 
     DV(QV1,v) denotes a difference vector between the query vector QV1 and a vector v of the experience matrix EX 1 . A value indicative of a difference between the query vector QV1 and a vector v of the experience matrix EX 1  may be determined based on the query vector QV1 and a vector v of the experience matrix EX 1 . The “difference” may expressed e.g. by an angle θ between the query vector QV1 and the vector v of the experience matrix EX 1 . The “difference” may expressed e.g. by the cosine cos(θ) of the angle θ between the query vector QV1 and the vector v of the experience matrix EX 1 . The cosine (cos(θ)) of the angle θ between two vectors v and QV1 may be calculated from the dot product, by using the equation |v∥QV1|cos(θ)=v·QV1. The difference may expressed e.g. by the Euclidean length |DV| of the difference vector DV. The difference may expressed e.g. by the dot product QV1·v of the vectors. 
     The difference may expressed e.g. by the square |DV| 2  of the Euclidean length |DV| of the difference vector DV. The difference may expressed e.g. as the taxicab length (Manhattan length) of the difference vector DV. Also other metrics may be used when defining the length of the difference vector DV. Also other metrics may be used when evaluating the difference between the vectors. 
     One or more prediction output words may now be selected from the vocabulary VOC1 based on the differences between the query vector QV1 and the vectors of the experience matrix EX 1 . If the difference between the query vector QV1 and a candidate vector fulfils a selection criterion, the word associated with said candidate vector may be provided as a prediction word. 
     The differences DV may be compared with each other in order to find the sparse vector or vectors which deviate by the smallest distance DV from the query vector QV1. In particular, the differences DV may be sorted. A word associated with a sparse vector having the smallest distance DV may be provided as the output OUT1 of the prediction method. The output may be called as the prediction. Also several words associated with sparse vectors having the smallest distance DV may be provided as the output OUT1. For example, N P  words associated with candidate vectors having the smallest distance DV may be provided as the output OUT1, wherein the integer N P  may be e.g. in the range of 2 to 10. 
     In the example of  FIG. 3   a , the smallest difference values (|DV| 2 =6) are associated with the vectors v P , v k  and v n−2 . If the number N P  is set to be equal to three, the words “mail”, “meeting” and “silent” may be provided as the prediction words. 
     The query words Q1, Q2 are already known to describe the situation. The query words Q1, Q2 may be excluded from the prediction words OUT1. Vectors associated with the query words Q1, Q2 may be excluded from the comparison when the query vector QV1 is compared with the other vectors of the experience matrix EX 1 . 
     The prediction word or words may be interpreted to be an answer to a conditional question “which prediction word or words OUT1 are likely to describe a situation if the situation is already described by the one or more (known) query words Q1, Q2. 
     In the example of  FIG. 3   a , the prediction words were “mail”, “meeting” and “silent”, as determined from a single query word Q1 “morning”. One or more of these prediction words may be used for controlling a system. 
     For example, a system could automatically activate an application for receiving and sending e-mails in a situation, which can be described by the word “morning”. For example, a system could automatically set itself into a silent mode of operation in a situation, which can be described by the word “morning”. 
     The one or more prediction words could be communicated back to a client making the query. The one or more prediction words could be communicated to a different client. The system may be arranged to utilize all prediction words for the control, or the system may be arranged to utilize a smaller subset of the prediction words for the control, wherein one or more prediction words may be ignored. 
       FIG. 3   c  shows making a query by using two or more query words Q1, Q2. Increasing the number of query words Q1, Q2 of a single query may improve the probability that the prediction word or words will be valid descriptors for the situation. In this example, the query consists of two words Q1, Q2. A first vector v k  of the experience matrix EX 1  associated with the query word Q 1  (e.g. morning) may be found by using the vocabulary VOC1. A second vector v n−1  associated with the query word Q 2  (e.g. work) may be found by using the vocabulary VOC1. The query vector QV1 may now be determined by combining the vectors v k , v n−1  associated with the query words Q1, Q2. For example, the query vector QV1 may be determined as a linear combination of the vectors v k , v n−1  associated with the query words Q1, Q2. In particular, the query vector QV1 may be determined as the sum of the vectors v k , v n-1 . The query vector QV1 may be formed e.g. by selecting the elements from the vectors v k  and v n−1  having maximum absolute value into the query vector QV1, or by another method of combining the vectors. The prediction words may be subsequently determined by comparing the query vector QV1 with the vectors v 1 , v 2 , . . . v n  of the experience matrix EX 1 , as described above for the case of  FIG. 3   a.    
     The prediction words may be subsequently by a method comprising:
         determining a first difference between the query vector QV1 and a first vector of the experience matrix EX 1 ,   determining a second difference between the query vector QV1 and a second vector of the experience matrix EX 1 , and   comparing the first difference with the second difference.       

     Vectors v k+1 , v n−1  of the experience matrix EX 1  associated with the query words Q1, Q2 may be excluded from the comparison. 
     In this case, the vector v P  of the experience matrix EX 1  appears to provide a difference vector DV having the shortest length (|DV| 2 =2). In this case, the prediction word corresponding to the vector v P  is “mail”. 
     Also several words associated with N P  vectors having the shortest distance vector DV to the query vector may be provided as the prediction. The number N P  may be e.g. three. In this case, the words “mail”, “meeting” and “silent” may be provided as the prediction words. 
     The updating method shown in  FIGS. 1   a - 2  was based on representing individual words w 1 , w 2 , . . . w n  by different basic sparse vectors a 1 , a 2 , . . . a n .  FIGS. 4   a  and  4   b  illustrate another way of storing co-occurrence data in an experience matrix EX 1 . The updating method shown in  FIGS. 4   a  and  4   c  is based on representing bags by basic sparse vectors. 
       FIG. 4   a  shows three bags BAG1, BAG2, BAG3 of words. The bags may be e.g. the same as in  FIG. 1   b.    
     Each bag BAG1, BAG2, BAG3 may be associated with a basic sparse vector b 1 , b 2 , b 3 . Each bag BAG1, BAG2, BAG3 may be associated with a different basic sparse vector b 1 , b 2 , b 3  such that all words of a single bag (e.g. BAG1) are associated with the same basic sparse vector (e.g. b 1 ). 
     The basic sparse vectors b 1 , b 2 , b 3  may fulfill the same criterions as the basic sparse vectors shown in  FIG. 1   a.    
       FIG. 4   b  shows updating the experience matrix EX 1  by using co-occurrence data derived from the bag BAG1. The bag contains two or more words W 1 , W 2 , W 3  (e.g. the words “morning”, work” and “mail”). Each word W 1 , W 2 , W 3  of the bag BAG1 is now represented by the same basic sparse vector (e.g. b 1 ). The words W 1 , W 2 , W 3  of the bag BAG1 are the same as the words w P , w k+1 , w n−1  of the vocabulary VOC1. This allows finding the vectors v P , v k+1 , v n−1  of the experience matrix EX 1  associated with the words of the bag BAG1. These vectors may be called as the target vectors. 
     The experience matrix EX 1  may be initially a zero matrix (null matrix) but this is not necessary. The initial values of several vectors of the experience matrix EX 1  may exhibit smooth spatial variation. The matrix EX may already contain vectors obtained as linear combinations of previous vectors of the matrix EX 1  and sparse vectors. 
     The basic sparse vector b 1  representing the bag BAG1 may now be added to each target vector v P , v k+1 , v n−1  associated with a word of the bag BAG1. The same basic sparse vector b 1  is now common to all words of the bag BAG1. The same basic sparse vector b 1  may be added to all target vectors v P , V k+1 , v n−1  associated with the words of the bag BAG1. In general, a modified target vector associated with a word of the bag BAG1 may be formed as a linear combination of the target vector associated with said word and the basic sparse vector b 1 . The second bag BAG2 may be represented by a different basic sparse vector (e.g. b 2 ). The basic sparse vector b 2  representing the second bag BAG2 may now be added to each target vector associated with a word of the bag BAG2. The third bag BAG3 may be represented by a different basic sparse vector (e.g. b 3 ). The basic sparse vector b 3  representing the third bag BAG3 may now be added to each target vector associated with a word of the bag BAG3. 
     Thus, the experience matrix EX 1  may be updated by using contents of a plurality of bags BAG1, BAG2, BAG3. Several vectors of the experience matrix EX 1  may eventually be linear combinations of different sparse vectors b 1 , b 2 , b 3 . 
       FIG. 4   c  shows an experience matrix EX 1  obtained after the co-occurrence data of the bags BAG1, BAG2, BAG3 has been stored in the experience matrix EX 1  by using different basic sparse vectors b 3  representing the bags. The sum of all elements e ik  of the matrix EX 1  may be equal to zero. e ik  denotes an element of the experience matrix EX 1  belonging to the column and to the k th  row. The value of the element e ik  may be an integer in order to maximize data processing speed. The value of the element e ik  is not limited to the range −1 to 1. 
     The experience matrix EX 1  determined by using the method shown in  FIG. 4   b  may be used for determining prediction words by using the methods shown in  FIGS. 3   a - 3   c.    
     The experience matrix EX 1  may have the same number (m) of columns and the same number (m) of rows as was discussed with reference to  FIG. 1   c.    
     An individual element e ik  of the experience matrix EX 1  may have an integer value. The integer value may also be greater than 1 (e.g. 2) or smaller than −1 (e.g. −2). 
     When using the updating method shown  FIGS. 4   a  and  4   b , i.e. when associating all words of a bag with a common sparse vector, the non-zero element values of the resulting experience matrix EX 1  may be distributed in a more uniform way among the columns of the experience matrix EX 1 , when compared with the updating method shown in  FIG. 2 . This may facilitate e.g. storing the values in the experience matrix EX 1  and/or comparison of a query vector with the vectors of the experience matrix EX 1 . 
     When using the updating method shown in  FIG. 2 , i.e. when associating words of a bag with sparse vectors defined by the vocabulary, each word is associated with the sparse vector of the basic matrix RM1 ( FIG. 1 ) as specified by the vocabulary VOC1. If a certain word occurs very frequently in the bags, this may sometimes result as high element values appearing in the experience matrix EX 1 . 
       FIGS. 5   a - 5   c  show collecting words from a buffer to a single bag. Words may be received from one or more clients and/or from the system. The received words may be (temporarily) stored in one or more buffers. The words may be collected from the buffers to a bag. The experience matrix may be updated by using the contents of the bag. The experience matrix may be subsequently updated by using the contents of a second (different) bag. 
     In  FIG. 5   a , the words W 1,t1 , W 2,t1 , W 3,t1  of a bag may represent the same instant t 1 . The bag may contain words representing a single instant. 
     However, information about temporal relationships may be added to the experience matrix by using a bag, which contains words representing the state of the system at two or more different time instances t 1 , t 2 . Bags gathered by this kind of temporal combining (temporal “pairing”) may also be utilized e.g. for evaluating the probability for a consecutive second state if the system is previously in a first state. 
     In  FIG. 5   b , the words W 1,t1 , W 2,t1 , W 3,t1  W 1,t2 , W 2,t2 , W 3,t2  of a bag may represent two or more instants t 1 , t 2 . A single bag may contain words representing two or more different instants t 1 , t 2 . In case of  FIG. 5   b , the number of words in a single bag may be greater than the number of words representing a single instant t 1  or t 2 . 
     The time period between the instants t 1  and t 2  may be called as a time span. 
     In  FIG. 5   c , the words W 1,t1 , W 2,t1 , W 3,t1 , W 1,t2 , W 2,t2 , W 3,t2  of a bag may represent two or more instants t 1 , t 2 . The bag may contain words representing two or more different instants t 1 , t 2 . The collecting of words shown in  FIGS. 5   b  and  5   c  may be used e.g. when the aim is to gather information about temporal relationships between words. The collecting of words shown in  FIGS. 5   b  and  5   c  may be used e.g. when the aim is to gather information about temporal relationships between states of a system. 
     The method of  FIG. 5   b  may be used e.g. when there is no earlier knowledge about the relevance of the words and/or no earlier knowledge about the temporal relationships of the words. The method of  FIG. 5   c  may be used e.g. when some previous knowledge about causal or temporal relationships of the words is available. For example, The words W 1,t1 , W 2,t2  may be collected to the same bag if the value of the word W 2,t2  is known to depend on the value of the word W 1,t1 , the instant t 2  being later than the instant t 1 . 
     The word W 1,t1  could describe e.g. the weather conditions at the time t 1  (e.g. “raining” at the time 14:00), and the word W 2,t2  could describe e.g. a marking in the calendar of a user (e.g. “sports” at 18:00). The prevailing weather conditions may be received e.g. from an internet service. In this case the weather conditions prevailing at 14:00 might have a causal effect on whether the user will be truly practicing sports outside at 18:00. In this sense, it might be useful to collect the earlier word “raining” and the later word “sports” into the same bag. 
       FIG. 6  shows a system for storing co-occurrence data to an experience matrix. System words describing time may be received e.g. from a clock. System words describing location (of a portable device) may be received e.g. from a GPS navigation unit (GPS means Global Positioning satellite System). System words describing the acceleration (of a portable) device may be received from an accelerometer. Words may also be received from other physical sensors. Client words may be received from one or more clients. 
     The term “pull” may mean that communication of data from the sensor to the buffer may take place such that the communication is not initiated by the sensor. In an embodiment, the sensor may provide a system word whenever requested. In an embodiment, communication of data from the sensor does not start updating the experience matrix. 
     The term “push” may mean that communication of data from a client to the buffer may be initiated by the client. In an embodiment, communication of data from the client may also initiate updating the experience matrix. 
     The term “flush” may mean updating the experience matrix by using one or more bags of words. The bags may be collected from the contents of the buffer. 
     The experience matrix may also be used when providing a prediction, as described above (See the discussion related to  FIGS. 3   a - 3   c ). 
       FIG. 7   a  shows a subsystem  400  for processing co-occurrence data. The subsystem  400  may be arranged to store co-occurrence data in an experience matrix EX 1 . The subsystem  400  may be arranged to provide a prediction based on co-occurrence data stored in the experience matrix EX 1 . 
     The subsystem  400  may comprise a buffer BUF1 for receiving and storing words, a collecting unit WRU for collecting words to a bag, a memory MEM1 for storing words of the bag, a sparse vector supply SUP1 for providing basic sparse vectors, memory MEM3 for storing the vocabulary VOC1, the vocabulary stored in the memory MEM3, a combining unit LCU1 for modifying vectors of the experience matrix EX 1  and/or for forming a query vector QV1, a memory MEM2 for storing the experience matrix EX 1 , the experience matrix EX 1  stored in the memory MEM2, a memory MEM4 for storing the query vector QV1, and/or a difference analysis unit DAU1 for comparing the query vector QV1 with the vectors of the experience matrix EX 1 . The subsystem  400  may optionally comprise a buffer BUF2 and or a buffer BUF3 for storing a query Q1 and/or a prediction OUT1. 
     The words may be received from one or more sensors NAV1, G 1 , from a clock CLK1 and/or from one or more clients C1. The words may be collected to individual bags by a collector unit WRU1. The words of a bag may be collected (i.e. temporarily stored) in the memory MEM1. The contents of each bag may be communicated from the memory MEM1 to a sparse vector supply SUP1. The sparse vector supply SUP1 may be configured to provide basic sparse vectors for updating the experience matrix EX 1 . 
     The contents of each bag and the basic sparse vectors may be communicated to a combining unit LCU1, which may be configured to modify the vectors of the experience matrix EX 1  (e.g. by forming a linear combination). In particular, the combining unit LCU1 may be configured to add basic sparse vectors to target vectors specified by the words of each bag. The combining unit LCU1 may be arranged to modify the first vector (v 1 ) by forming a linear combination of the first vector of the matrix (EX 1 ) and one or more sparse vectors (a 2 , b 1 ). 
     The combination unit LCU1 may be arranged to execute summing of vectors at the hardware level. Electrical and/or optical circuitry of the combination unit LCU1 may be arranged to simultaneously modify several target vectors associated with words of a single bag. This may allow high data processing rate. 
     The experience matrix EX 1  may be stored in the memory MEM2. The words may be associated with the vectors of the experience matrix EX 1  by using the vocabulary VOC1 stored in the memory MEM3. Also the vector supply SUP1 may be configured to use the vocabulary VOC1 (or a different vocabulary) e.g. in order to provide basic sparse vectors associated with words of a bag. 
     The subsystem  400  may comprise the combining unit LCU1 or a further combining unit LCU2 (not shown) configured to form a query vector QV1 based words of a query Q1. The query vector QV1 may be formed by combining vectors of the experience matrix EX 1 . The query vector QV1 may be formed as a linear combination of vectors of the experience matrix EX 1 . The locations of the relevant vectors of the experience matrix EX 1  may be found by using the vocabulary VOC1. The query vector QV1 may be stored in the memory MEM4. 
     The difference analysis unit DAU1 may be configured to compare the query vector QV1 with vectors of the experience matrix EX 1 . A difference analysis unit DAU1 may be arranged to determine a difference between a vector of the experience matrix EX 1  and the query vector QV1. The difference analysis unit DAU1 may be arranged to sort differences determined for several vectors. The difference analysis unit DAU1 may be configured to provide a prediction OUT1 based on said comparison. 
     The query words Q1, Q2 itself may be excluded from the prediction words. 
     The difference analysis unit DAU1 may be arranged to compare the vectors at the hardware level. Electrical and/or optical circuitry of the combination unit LCU1 may be arranged to simultaneously determine quantitative difference descriptors (DV) for several vectors of the experience matrix EX 1 . This may allow high data processing rate. 
     The subsystem  400  may comprise a control unit CNT1 for controlling operation of the subsystem  400  and/or for controlling operation of the system  500  (see  FIG. 11 ). The control unit CNT may comprise one or more data processors. The subsystem  400  may comprise a memory MEM5 for storing program code PROG1. The program code PROG1 when executed by one or more data processors may be for carrying out the method of the invention. 
     Words may be received e.g. from one or more clients C1, from one or more sensors G 1 , from a position sensor NAV1, and/or from a clock CLK1. The prediction word or words OUT1 may be communicated to the client C1 or to a different client. The client C1 may also retrieve system words from the buffer BUF1 e.g. in order to form a query Q1. 
       FIG. 7   b  shows, by way of example, how a word may be provided based on physical interaction between a sensor and its environment. A sensor G 1  may provide one or more electrical or optical sensor signals S 0  by monitoring its physical environment. The monitoring comprises passive or active interaction with the physical environment. For example, in case of passive interaction, a microphone or a light sensor may receive sound or light waves (which are not initiated by the system). The signal S 0  may be e.g. an analog signal representing the magnitude and frequency of a sound wave received by a microphone. The signal S 0  may be e.g. an analog signal representing the magnitude and frequency of vibrations detected by an acceleration sensor. 
     In case of active interaction, the sensor G 1  may transmit e.g. ultrasound or infrared light, which may be reflected from a surface of the environment. For example, the distance to the surface may be estimated e.g. based on the reflected sound or light waves received by a microphone or a light sensor. Optionally, a digital sensor signal S 1  may be provided by processing the (analog) signal S 0  in a sensor interface GIN1. The digital sensor signal S 1  may comprise e.g. spectral analysis of a sound received by a microphone. The digital sensor signal S 1  may comprise a digital image captured by an image sensor. 
     Some sensors may directly provide a quantized digital signal, which may be directly used as a system word. For example, a microswitch proximity sensor may or a digital encoder of a joystick may directly provide digital words representing state of a system. For example, a microswitch may provide either a word “1” or a word “0” specifying whether something is pressing the switch or not. 
     Optionally, a quantizer QU1 may be arranged to provide a quantized sensor signal S 2  based on the digital sensor signal S 1 . The quantization may be performed by using a mapping function, which may be modifier later, if needed. For example, sound volume values ranging from 0 to 127 (128 different values) may be mapped into a smaller number of values (e.g. 0, 1, 2). 
     Optionally, the quantizer QU1 may comprise an analyzer, which is arranged to classify the signal S 1  into two or more different classes. The quantizer QU1 may be a classifier. The quantizer QU1 may provide a value specifying the class of the signal S 1 . For example, the quantizer QU1 may be arranged to provide values, which specify the class of a sound based on spectral analysis (e.g. “0”=motor, “1” music, “2” human voice). 
     A value provided by the quantizer QU1 may be used as an input word for the subsystem  400 . Optionally the value may be converted to a (different) word e.g. in order to make it more easily intelligible to a human user. 
     The quantized sensor signal S2 may be optionally converted into a different word which describes the physical environment of the sensor in a natural language (e.g. in the English language or in Finnish language). The signal S2 may be converted into the word by using a dictionary. The contents of the dictionary may be fixed or it may be updated at a later stage. Numerical words (0,1,2) describing the nature of a sound may be converted into words of a natural language e.g. by using the following dictionary “0”—“motor”, “1”—“music”, “2”—“voice”. Numerical words (0,1,2) describing the volume of a sound may be converted into words of a natural language e.g. by using the following dictionary “0”—“silent”, “1“—”normal”, “2”—“loud”. 
     Optionally, a marker unit MRK1 may be arranged to modify a word by adding an identifier, which makes the word unique and different from other words. The identifier may e.g. specify the identity of the sensor S1 or the type of the quantity specified by said word. For example, when the word is a numerical word (e.g. “0”, “1” and “2”) describing sound volume, a prefix “volume” may be attached to the word so as to form e.g. a word “volume 0”. 
     Thus, a sensor S1 may be arranged to provide a sensor word (system word) by using one or more method steps described above. 
     In an embodiment, an analysis unit receiving a signal from an acceleration sensor may be arranged to determine e.g. whether a portable device is stationary, carried by a walking person, carried by a running person, or carried in a moving vehicle. The analysis unit may provide words, e.g. “stationary”, “walking”, “running”, “traveling” describing these different states. The acceleration sensor may be e.g. a capacitive or a piezoelectric acceleration sensor. 
     However, the signal obtained from sensor G 1  does not need to be converted into a sensor word having a clear semantic meaning, i.e. it is not necessary to use the dictionary THESA1. In an embodiment, an analysis unit receiving a signal from an acceleration sensor may be arranged to provide sensor words describing different acceleration conditions, e.g. “acceleration A”, “acceleration B”, and “acceleration C”. A system  500  comprising the subsystem  400  and the sensor G 1  may be operated such that the system  500  can make successful predictions even if the semantic meaning of a sensor word is not known. 
     A word provided by a sensor G 1  may be presented e.g. as a uniform resource identifier (URI) containing a scheme and a scheme specific part. For example, a word provided by using an acceleration sensor may be e.g. “motion://moving” or “motion://stationary”, where the first part “motion” is the scheme, and the second part “moving” or “stationary” is the scheme specific part. The parts may be separated by the symbols “://”. A word provided by using the acceleration sensor may also be e.g. “orientation://vertical” or “orientation://horizontal” 
     Referring to  FIGS. 7   a - 7   c , the sparse vector supply SUP1 may provide a sparse vector e.g. by retrieving a previously generated sparse vector from a memory (table) and/or by generating the sparse vector in real time. 
     Referring to  FIG. 7   c , the sparse vector supply SUP1 may comprise a memory for storing basic sparse vectors a l , a 2 , . . . a n  associated with words of the vocabulary VOC1 (see e.g.  FIG. 1   a ). The basic sparse vectors a 1 , a 2 , . . . a n  may form a basic sparse matrix RM1. The basic sparse vectors a 1 , a 2 , . . . a n  may be previously stored in a memory of the sparse vector supply SUP1. Alternatively, or in addition, an individual basic sparse vector associated with a word may be generated in real time when said word is used for the first time in a bag. The basic sparse vectors may be generated e.g. by a random number generator. 
     The configuration of  FIG. 7   c  may be used e.g. when carrying out the updating to method shown in  FIGS. 1   a  to  2 . 
     Referring to  FIG. 7   d , the sparse vector supply SUP1 may comprise a memory for storing a plurality of previously determined basic sparse vectors b 1 , b 2 , . . . When a new bag arrives, trigger signal may be generated, and a count value of a counter COUN1 may be changed. Thus a next basic sparse vector may be retrieved from a location of the memory indicated by a counter. Thus, each bag will be assigned a different basic sparse vector. The same basic sparse vector may represent each word of said bag, as described in the updating method of  FIGS. 4   a  and  4   b.    
     Referring to  FIG. 7   e , a new basic sparse vector b k  may be generated by a random number generator RVGU1 each time when a new bag arrives. Thus, each bag will be assigned a different basic sparse vector (the probability of generating two identical sparse vectors will be negligible). The same basic sparse vector may represent each word of said bag, as described in the updating method of  FIGS. 4   a  and  4   b.    
     Referring to  FIG. 7   f , a system  500  may comprise the subsystem  400  for storing co-occurrence data and/or for providing predictions. 
     The system may be configured to:
         provide one or more query words associated with a situation,   make a prediction by using an experience matrix and said one or more query words, and   control operation of said system based on said prediction.       

     The system  500  may optionally comprise one or more sensors G 1  for providing system words describing e.g. status of the system or a property of an environment of the system. The system  500  may optionally comprise a clock CLK1 for providing time data. The system  500  may optionally comprise a location detector NAV1 for providing location data. The location detector may be e.g. a GPS navigation unit. 
     Co-occurrence data may be stored in the experience matrix EX 1  as described above. 
     A client C1 may send a query Q1 to the subsystem  400 . The query Q1 may comprise e.g. a word provided by a human user via a user interface  501 , from an application APP1, and/or from a sensor G 1  of the system  500 . The query Q1 may comprise e.g. a word retrieved from an internet service (e.g. weather information). The subsystem  400  may provide one or more prediction words OUT1 based on the query Q1, as described above. The system  500  may be configured to start and/or stop an application APP1, APP2 based on a prediction OUT1. The operation of the system  500  may be controlled based on the prediction OUT1. The prediction OUT1 may be used e.g. as an input for a web browser. The system  500  may be configured to display information on a display of a user interface  501  based on the prediction OUT1 (user interface management). The system  500  may be configured to set an operating mode based on the prediction OUT1. The system  500  may be configured to allocate data processing power to different applications and/or units based on the prediction OUT1. The system  500  may be configured to start and/or stop operation of a functional (physical) unit of the system (e.g. a GPS navigation unit or an audio amplifier) based on the prediction OUT1. 
     Operation of a first device of the system  500  may be controlled based on words obtained from a second device of the system  500 . For example, the first device may be carried by the user (a first person), and the second device may be carried by a second person. The second person may be e.g. a family member, a friend, or a workmate of the first person. The query Q1 may comprise one or more words related to the status of the second device and/or related to the calendar of the second person. The system may now provide a prediction OUT1 based on the query Q1. The system may propose activation of a functionality based on the prediction OUT1. 
     For example, if the second device has been set into the silent mode, the system,  500  may suggest based on the prediction that the preferred way of contacting the second person might be e.g. a SMS message or e-mail message, instead of making a phone call. The experience matrix EX 1  may store co-occurrence data, which indicates that an attempt to make a phone call has almost never been successful when the second device has been set into the silent mode. The experience matrix EX 1  may store co-occurrence data, which indicates that the user of the second device has sometimes immediately responded to an e-mail message even when the second device has been set into the silent mode. Thus, when the user of the first device attempts to make a phone call to the second person, the system  500  may propose activating an application for sending messages to the second device (e.g. SMS message or e-mail). 
       FIGS. 8   a - 8   c  show an example for controlling operation of a communications system by using predictions. 
     The experience matrix EX of the system  500  may be updated by using the bags BAG4 to BAG9 shown in  FIG. 8   a . In this example, the bags BAG4 and BAG7 contain the words “meeting”, “Person A” and “silent mode”. The bags BAG5 and BAG8 contain the words “meeting”, “Person B” and “teleconference with person C”. The bags BAG6 and BAG9 contain the words “meeting”, “Person C” and “normal mode”. The bags BAG4-BAG9 also contain words specifying time and the day of the week. 
     Referring to  FIG. 8   b , the system  500  may determine e.g. based on a marking in the calendar that a meeting with person A is scheduled to start at 9:00. Based on the experience, the words “meeting” and “Person A” often appear together with the word “silent mode”. This co-occurrence data has been already stored in the experience matrix EX 1 . A client of the system  500  may form a query Q1 containing the words “9:00”, “meeting”, “Person A”. The subsystem  400  may provide a prediction based on the query G 1 ″ by using the experience matrix EX 1  comprising the co-occurrence data of FIG.  8   a . In this example, the prediction provided by the subsystem  400  may comprise e.g. the word “silent mode”. Also the time and/or date specified by words of a query Q1 may have an effect on the prediction result. For example, meetings held a specific time and/or date may appear to be associated e.g. with “playing video”. However, in this example, the dates and times of the bags are distributed so that it is not yet possible to detect that kind of an association. 
     When the meeting is about to start (e.g. at the time 8:59), the system  500  may propose changing the operation mode (“profile”) to the silent mode e.g. in order to avoid disturbing the meeting with incoming telephone calls. One or more information fields F1-F4 may be displayed to the user. A field F1 may propose changing to the silent mode. The user or accept or reject the proposition e.g. by touching the (virtual) key(s) B1 or B2. In an embodiment the key B2 may be omitted. If the user does not touch the key B2 within a predetermined time period, the system may automatically change to the silent mode. In an embodiment the key B1 may be omitted. If the user does not touch the key B1, the system may continue operation in the normal mode. In an embodiment both keys B1, B2 may be omitted. The user may have previously authorized the system to set the operating mode automatically based on the prediction. 
     The fields F2-F4 may display auxiliary information. The field F3 may optionally display e.g. the actual time. The field F2 may optionally display e.g. the next relevant event (e.g. meeting with person A). The field F4 may optionally display e.g. a calendar view. In addition to setting the operating mode, the system  500  may also control displaying fields F1-F4, and/or displaying the keys B1, B2 based on the prediction. 
     Thanks to controlling operation based on the prediction, the user may now set the system to the silent mode by touching one key only. In an embodiment, the user does not need to do anything in order to set the system to the silent mode. 
     Without the prediction, the user might need to seek a suitable menu from the menu structure of the system in order to set the system to the silent mode. 
     Typically, this operation would require making and confirming several selections in the menus of the menu structure of the user interface  501 . 
     Referring to  FIG. 8   c , the system  500  may determine e.g. based on a marking in the calendar that a meeting with person B is scheduled to start at 13:00. 
     Based on the experience, the words “meeting” and “Person B” often appear together with the word “teleconference with person C”. This co-occurrence data has already been stored in the experience matrix EX 1 . 
     A client of the system  500  may form a query Q1 containing the words “9:00”, “meeting”, “Person B”. The subsystem  400  may provide a prediction based on the query G 1 ″ by using the experience matrix EX 1  comprising the co-occurrence data of  FIG. 8   a . In this example, the prediction provided by the subsystem  400  may comprise e.g. the word “teleconference with person C”. When the meeting is about to start (e.g. at the time 12:59), the system  500  may propose starting a teleconference with person C. One or more information fields F1-F4 may be displayed to the user. A field F1 may propose starting a teleconference with person C. The user or accept or reject the proposition e.g. by touching the (virtual) key(s) B1 or B2. 
     If the user accepts the proposition, the system may automatically start a teleconference. This may comprise automatically activating a camera module for capturing video images of the user. This may comprise (automatically) opening a video communication link and/or audio communication link with an interface of the person C at a remote location. 
     In an embodiment the key B2 may be omitted. If the user does not touch the key B2 within a predetermined time period, the system may automatically open the telecommunication link. In an embodiment the key B1 may be omitted. If the user does not touch the key B1, the system does not open the communication link. In an embodiment both keys B1, B2 may be omitted. The user may have previously authorized the system to open the telecommunication link automatically. 
     Thanks to controlling operation based on the prediction, the user may now open the communication link by touching one key only. In an embodiment, the user does not need to do anything in order to open the communication link. 
     Without the prediction, the user might need to seek a suitable menu from the menu structure of the system in order to open the telecommunication link. Typically, this operation would require making and confirming several selections in the menus of the menu structure of the user interface  501 . 
       FIG. 8   d  shows method steps for updating the experience matrix EX and for controlling the system based on the prediction. In step  705 , a scheduled event or an actual event may be stored in a memory of the system. In particular a calendar event may be added to the memory e.g. via the interface  501  by a user or by another person. In step  710 , the user or another person may set an operating mode of the system, associated with the event mentioned in step  705 . In step  715 , the user or another person may start and/or stop one or more applications, associated with the event mentioned in step  705 . In step  720 , words describing the event, operating mode and/or applications may be collected into a bag. An experience matrix EX 1  of the system  500  may be updated by using the bag. Co-occurrence data representing previous events may already be stored as the (sparse) vectors of the matrix EX 1  before this step, i.e. the matrix does not need to empty prior to step  720 . The steps  705 - 720  may be repeated several times in order to gather co-occurrence data related to several different events. 
     In step  750 , the system may form a query Q1 comprising a word describing an event. The query Q1 may also comprise a word specifying additional information associated with the event, e.g. an identifier of a person, who is associated with the event. In step  755 , the subsystem  400  may provide a prediction by using the query Q1 and the vectors previously stored in experience matrix EX 1 . In step  760 , the system  500  may e.g. propose starting and/or stopping one or more applications and/or it may propose setting an operating mode based on the prediction. 
     In step  765 , the system may request permission from the user to carry out the action proposed in step  760 . In an embodiment, the user may have given the permission in advance. In step  770 , the response given by the user may recorder in a memory and used for updating the experience matrix EX 1 . In particular, a word describing the response may be collected in the same bag together with one or more other words related to the query Q1. The words of the bag may be used for updating the experience matrix EX 1 . In step  775 , the operating mode may be set according to the prediction, if this was accepted by the user in step  765 . In step  780 , one or more applications may be started and/or stopped according to the prediction, if this was accepted by the user in step  765 . 
     The steps  705 - 780  may be repeated several times. The steps  705 - 780  may be repeated e.g. several times per day during the lifetime of a portable device belonging to the system  500 . The lifetime may be several years, e.g. more than three years. Thus, the experience matrix EX 1  may eventually contain co-occurrence data representing e.g. more than 1000 events (data representing more than 1000 bags). 
     The memory MEM2 containing the experience matrix EX 1  may be included in a first portable device carried by a user. The first portable device may be called e.g. as a smart phone and/or as a portable computer (which may have wireless communication capabilities). The first portable device may be e.g. one of the devices  1260 ,  1251 ,  1250  shown in  FIG. 11 . 
     Sooner or later, the first portable device may become outdated, it may be lost, or it may be broken. A (back-up) copy of the experience matrix EX 1  may be stored in the system  500  in a location, which is remote and/or separate from the location of the memory MEM2. The experience matrix EX 1  containing the previous data may be easily copied to one or more portable devices, if needed. 
     An experience matrix EX 1  may be copied from the device of a first person to a device of a second person. An experience matrix EX 1  may be transferred or copied from one device to another device e.g. via internet, via en electrical cable, via an optical cable, via a radio frequency link, via a mobile telephone network, or by using a physical memory (i.e. a computer memory product) storing the experience matrix EX 1 . The copying may be associated with a payment, i.e. the experience matrix EX 1  may also be sold as an individual item, separately from the original system  500  which was used for collecting the data into the matrix EX 1 . An experience matrix EX 1  may be wholly or partially transferred from one device to another, and may, but does not have to replace partly or wholly a destination matrix (i.e. a second experience matrix). For example, a user may receive an update of an experience matrix related to a vacation trip, e.g. an experience matrix storing co-occurrences relevant for traveling in mountain areas of Italy. 
     The data stored in the experience matrix EX 1  is likely to be useful when the queries Q1 contain at least one same word which was used for updating the experience matrix EX 1 . Previous data stored in an experience matrix EX 1  may be applicable only in a certain type of systems, wherein the data may be substantially useless in a second type of a system, which uses different query words and/or operates in a fundamentally different environment. For example, an experience matrix EX 1  which only comprises data related to professional meetings is not likely to be useful for predicting which video clips the user wishes to view in his freetime. 
       FIG. 9   a  shows how an experience matrix EX may be represented by using hash tables. The majority of the elements e ik  of an experience matrix EX 1  may be zero elements. Several vectors of the experience matrix EX 1  may be zero vectors. In that case, it may be needless to use memory space for storing the zero values. The vocabulary VOC1 may be a hash table, wherein each word stored in the vocabulary VOC1 may be used as the key. Entries in the vocabulary VOC1 point to value arrays INDH, which contain the actual values of the non-zero elements e ik  of the experience matrix EX 1 . For example, an individual word w k  may point to a value array INDH k , which contains values of the non-zero elements of the vector v k  of the experience matrix EX, said vector v k  being associated with the word w k . All elements of the value array INDH k  may be non-zero. 
     A second hash table CAH1 may be used to keep track of those columns of the experience matrix, which contain non-zero elements. The second hash table CAH1 may be called e.g. as a “columns activated hash table”. The second hash table CAH1 may have the column number (i) as the key. Entries in the second hash table point to occurrence arrays OCCL, which in turn may contain a list of row numbers (k) of words (w k ) contributing to each column of the experience matrix EX 1 . For example, an occurrence array OCCL, may contain the row numbers k 1 , k 2 , k 3 , to indicate that the elements e at the column i and at the rows k 1 , k 2 , k 3  are non-zero. 
     The hash tables VOC1, CAH1, the group of the value arrays INDH and the group of the occurrence arrays OCCL may together fully specify the values and the locations of the non-zero elements of the experience matrix EX 1 . 
     A value array INDH may contain only the values of the non-zero elements of a single vector of the experience matrix EX 1 . It does not need to specify the indices of the columns of the experience matrix EX 1  containing said non-zero values, because this information may be derived from the occurrence arrays pointing to the word associated with said value array INDH. However, the value array INDH may contain additional information in addition to the values of the non-zero elements, e.g. the indices of the columns of the experience matrix EX 1  containing the non-zero values. The value arrays INDH may together form a value matrix. The occurrence arrays OCCL may together form an occurrence matrix. 
       FIG. 9   b  shows method steps for updating an experience matrix EX 1  represented by the hash tables. In this case, a predetermined group of words contained in the vocabulary VOC1 may be used in order to avoid changing the number of rows of the experience matrix EX 1 . Words not belonging to said predetermined vocabulary VOC1 may be ignored. In step  810 , a bag of words may be received. In step  830 , it may be checked whether a word of the bag is contained in the vocabulary VOC1. Words not contained in the vocabulary VOC1 may be ignored in step  820  in order to avoid changing the number of rows of the experience matrix EX 1 . In step  840 , a basic sparse vector representing each word of a bag may be determined by using the vocabulary VOC1 and the basic sparse matrix RM1 (see  FIG. 1   a ). Alternatively, a common (i.e. the same) sparse vector may be assigned to each word of a single bag (see  FIG. 4   a ). The element values stored in a value array INDH k  associated with a word w k  of the bag may be updated by using the basic sparse vector or vectors. The updating method described in  FIGS. 1   a  to  2  or the updating method described in  FIGS. 4   a  to  4   b  may be used. An individual element value may be increased, decreased, or have its previous value. 
     The number of non-zero elements of a vector of the experience matrix EX 1  may also need to be increased during the updating. Thus, the length of a value array INDH k  may be increased in order to store the additional values. The locations of the values stored in value array INDH k  may be in the same order as in the vector of the experience matrix EX 1  represented by said value array. This means that an element may be added also in the middle of a value array INDH k  and/or to an end of the value array INDH k . 
     In step  860 , the hash table CAH1 and the occurrence arrays OCCL may be updated according to the new elements, which were possibly added to the value array INDH. If a non-zero value was stored in an element e ik  in a column (i), which was previously a zero column, the hash table CAH1 may be updated to contain a pointer to an occurrence array OCCL, which in turn contains one or more pointers to the words where the column (i) was used. The hash tables VOC1, CAH1 and the arrays INDH and OCCL contain the co-occurrence data of an experience matrix EX 1 . An experience matrix EX 1  may be represented in a hash table format, by using the hash tables VOC1, CAH1 and the arrays INDH and OCCL. 
       FIG. 9   c  shows method steps for making a prediction by using the experience matrix EX 1 . The experience matrix EX 1  may be represented in a hash table format according to  FIG. 9   a . In step  910 , a query containing one or more query words Q1, Q2 may be received. In step  920 , vectors v of the experience matrix EX 1  associated with each query word Q1, Q2 may be identified by using the vocabulary VOC1. When the experience matrix EX 1  is represented in the hash table format, the non-zero values of the vectors may be specified by an array INDH. 
     In step  930 , a query vector QV1 may be formed. In case of a single query word Q1, the associated vector of the experience matrix EX 1  may be used as the query vector QV1 as such. In case of a query comprising two or more query words Q1, Q2, the query vector QV1 may be formed as a combination of the vectors identified in step  930 . In particular, the query vector QV1 may be formed as a sum of the vectors identified in step  930 . 
     In step  940 , the query vector QV1 determined in step  930  may be compared with the vectors of the experience matrix EX 1 . The comparing may comprise calculating a difference between the query vector QV1 and each vectors of the experience matrix EX 1 . When the experience matrix EX 1  is represented in the hash table format, the non-zero values of the vectors may be specified by an array INDH. In step  950 , one or more words associated with one or more vectors having the smallest difference to the query vector QV1 may be selected and provided as the prediction words. The prediction words may be used for controlling the operation of the system  500 , as described above. 
     Thus, the experience matrix (EX 1 ) may be represented by using hash tables (VOC1, IND, CAH1, OCCL) such that a vector (v 1 ) of the matrix (EX 1 ) has a non-zero element (e ik ) at a column (i) of the matrix (EX 1 ), and a hash table (OCCL i ) contains a pointer identifying a word (w k ) of a vocabulary (VOC1) associated with the vector (v k ). The system  500  or an apparatus of the system  500  may be configured to represent the experience matrix (EX 1 ) by using hash tables (VOC1, IND, CAH1, OCCL) such that a vector (v 1 ) of the matrix (EX 1 ) has a non-zero element (e ik ) at a column (i) of the matrix (EX 1 ), and a hash table (OCCL i ) contains a pointer identifying a word (w k ) of a vocabulary (VOC1) associated with the vector (v k ). 
     Sometimes an element value stored in the array INDH may become zero during updating the experience matrix EX 1 . In an embodiment, the zero element may be removed from the array INDH in order to minimize consumption of memory space. The table CAH1 and the array OCCL corresponding to the removed element may be updated, respectively. 
       FIG. 10   a  shows generating one or more auxiliary words T2-T6 based on one or more original words T1. Using the auxiliary word instead of the original word or in addition the original word may sometimes be more useful when updating the experience matrix EX 1  and/or when making a prediction. 
     The original word may be e.g. a string “2 Jan. 2012 09:03”. In principle, another substantially string “2 Jan. 2012 09:04” would be interpreted to a completely different word. This might reduce the efficiency of updating and using the experience matrix EX 1 . 
     The aim of the updating operations might be e.g. to gather co-occurrence data, which allows predicting actions, which are likely to be executed in a certain day of a week. For this aim, the original word “2 Jan. 2012 09:03” may be replaced or supplemented with an auxiliary word T5, which specifies the day of the week (Monday) corresponding to the date 2 Jan. 2012. The auxiliary word T5 may be determined from the original word e.g. by using a calendar. 
     The time expression contained in the original word “2 Jan. 2012 09:03” might have too high temporal resolution for some purposes. For example, if the aim is to predict what would be a suitable time to start e.g. a virus scanning application (which will consume battery power and data processing resources), an auxiliary word T6 may be determined such that the auxiliary word T6 represents the clock time with a lower resolution (e.g. “morning”) from the original word “2 Jan. 2012 09:03”. The auxiliary word may be provided e.g. by using a dictionary and/or by using a quantizer (classifier). 
     For example, the following words may be used to represent time: 
     time://late night (to represent times from 00:16 to 04:00)
 
time://early morning (to represent times from 04:01 to 06:00)
 
time://morning (to represent times from 06:01 to 11:45)
 
time://noon (to represent times from 11:46 to 12:15)
 
time://afternoon (to represent times from 12:16 to 17:00)
 
time://early evening (to represent times from 17:01 to 19:00)
 
time://evening (to represent times from 19:01 to 23:45)
 
time://midnight (to represent times from 23:46 to 0015)
 
     The original word may specify e.g. location. The location may be specified e.g. by using GPS coordinates and/or by providing a name of a location. One or more auxiliary words specifying a location may be determined from the original word e.g. by using an electronic map. For example, a first device of the system  500  may be located in a place called as “Vantaa” (in Finland), and a second device of the system  500  may be located in a place called as “Espoo” (in Finland). 
     For example, an auxiliary word “Southern Finland” or “Capital area of Finland” may be determined from the word “Vantaa” e.g. by using an electronic map or a location dictionary. 
     For example, an auxiliary word “Southern Finland” or “Capital area of Finland” may be determined from the word “Espoo” e.g. by using an electronic map or a location dictionary. 
     Thanks to the common auxiliary word, the co-occurrence data gathered by the first device may be used provide a prediction relevant to the user of the second device. 
     The electronic map may be e.g. downloaded from the internet. The one or more auxiliary words may be provided by a remote (internet) service. 
     The user of the system  500  may also associate a location with a name. For example, a portable device carried by the user may determine its location e.g. by a GPS navigation unit, and the device may also ask the use to give a name for the detected location. The name given by the user may be subsequently used as the word associated with said (GPS) location. The name may be e.g. “home”, “school”, “university”, or “working place”. Also a broader uniform resource locator (URL) may be determined based on a narrower uniform resource locator. In particular, a broader uniform resource locator of the internet may be determined based on a narrower uniform resource locator of the internet. 
     One or more auxiliary words T2, T3, T4 may be formed from the original word by tokenizing and/or parsing. The auxiliary word or words T2 to T6 may be used in a bag instead of or in addition to using the original word T1. 
     Referring to  FIG. 10   b , an auxiliary word GEN1 having a broader semantic meaning (“genus”) may be determined based on an original word SPEC1 having a narrower semantic meaning (“species”). The auxiliary word GEN1 having a broader semantic meaning (“genus”) may be determined from the original word SPEC1 by using a (semantic) dictionary DC1. For example, a word “meal” or “food” may be determined based on an original word “pizza”. The dictionary DC1 may be downloaded e.g. from an (internet) service. The auxiliary word GEN1 may be provided by a remote service, based on the original word communicated to the service. The system may be configured to determine a semantic ancestor GEN1 of an original word. The semantic ancestor GEN1 may be subsequently used as a word in a bag or as a part of a query. 
     Also an auxiliary word having a narrower semantic meaning (“species”) may be determined (by using a dictionary) based on an original word having a broader semantic meaning (“genus”). The system may be configured to determine a semantic descendant of an original word. This operation may be used for storing co-occurrence data e.g. in a situation where the original word is not contained in the vocabulary VOC1, but the term having the narrower semantic meaning is contained in the vocabulary VOC1. For example, a word “near 9 PM” may be generated based on an original word “evening”. However, this operation may sometimes involve a risk of adding partly erroneous information. 
       FIG. 11  shows, by way of example, a system  500  for gathering, storing and using co-occurrence data. The operation of the system  500  may be controlled based on a prediction determined by using the co-occurrence data stored as vectors in the experience matrix EX 1 . The system  500  may comprise one or more subsystems  400  for updating an experience matrix EX 1  and for providing predictions. Examples of the subsystem  400  were shown in  FIGS. 7   a  and  7   f . The system  500  may consist of a single device, or the system  500  may comprise a plurality of devices arranged to communicate with each other. A subsystem  400  may be implemented in a single device or in several devices arranged to communicate with each other. The system  500  may comprise a network service framework with one or more servers and one or more user devices. A subsystem  400  may be implemented in the network service framework with one or more servers and one or more user devices. 
     As shown in the example of  FIG. 11 , the different devices of the system  500  may be connected via a fixed network  1210  such as the Internet or a local area network (LAN). Alternatively or in addition, the devices may be connected via a mobile communication network  1220  such as the Global System for Mobile communications (GSM) network, 3rd Generation (3G) network, 3.5th Generation (3.5G) network, 4th Generation (4G) network, Wireless Local Area Network (WLAN), Bluetooth®, or other contemporary and future networks. Different networks may be connected to each other by means of a communication interface  1280 . A network ( 1210  and/or  1220 ) may comprise network elements such as routers and switches to handle data (not shown). A network may comprise communication interfaces such as one or more base stations  1230  and  1231  to provide access for the different devices to the network. The base stations  1230 ,  1231  may themselves be connected to the mobile communications network  1220  via a fixed connection  1276  and/or via a wireless connection  1277 . 
     There may be a number of servers connected to the network. For example, a server  1240  for providing a network service such as a social media service may be connected to the network  1210 . A second server  1241  for providing a network service may be connected to the network  1210 . A server  1242  for providing a network service may be connected to the mobile communications network  1220 . Some of the above devices, for example the servers  1240 ,  1241 ,  1242  may be arranged such that they make up the Internet with the communication elements residing in the network  1210 . 
     The system  500  may also comprise end-user devices such as one or more mobile phones or smart phones  1251 , one or more Internet access devices (Internet tablets)  1250 , one or more personal computers  1260 , a display or an image projector  1261  (e.g. a television), a video player  1262 , and/or a video camera  1263 . 
     These devices  1250 ,  1251 ,  1260 ,  1261 ,  1262  and  1263  can also be made of multiple parts. One or more devices may be connected to the networks  1210 ,  1220  via communication connections such as a fixed connection  1270 ,  1271 ,  1272  and  1280 . One or more devices may be connected to the networks  1210 ,  1220  via a wireless connection  1273 . One or more devices may be connected to the Internet via a wireless connection  1273 . One or more devices may be connected to the mobile network  1220  via a fixed connection  1275 . One or more devices may be connected to the mobile network  1220  via a wireless connection  1278 ,  1279  and/or  1282 . The connections  1271  to  1282  may be implemented by means of communication interfaces at the respective ends of the communication connection. 
     Referring to  FIG. 12   a , a user device  1251  may comprise a memory  1252 , one or more processors  1253 ,  1256 , and computer program code  1254  residing in the memory  1252  for implementing, for example, the functionalities of a software application like a browser or an application for sending and receiving messages. 
     The system  500  may comprise a user interface  501 . The user interface  501  may be implemented e.g. in a portable device, e.g. in a smart phone. The interface  501  may comprise e.g. a touch screen for visually displaying information and for receiving commands from a user. 
     The user device  1251  may comprise a user interface  501 . A user may receive information via the interface  501 . The user may control operation of the device  1251  and/or the system  500  by giving commands via the user interface  501 . The user interface may comprise hardware, e.g. a display, keypad and/or a touch screen. The user interface may comprise a display screen for viewing graphical elements displayed on the screen. The user interface may also comprise a software application e.g. for displaying various different virtual keys on a touch screen. 
     A user interface  501  may be implemented e.g. in a stationary or movable device, which contains a camera arranged to receive commands from a user based on gesture recognition. The device may comprise a microphone arranged to receive commands from a user based on voice recognition. The user does not need to be in (mechanical) contact with a part of the user interface  501 . 
     A user interface  501  may also be implemented in a device, which can be e.g. wrapped around the user&#39;s wrist (i.e. a wrist watch type device). A user interface  501  may be implemented e.g. in goggles (spectacles), which may comprise e.g. a virtual display for displaying information and/or a gaze direction detector to receive commands from a user by following his gaze direction. 
     The parts of the system  500  may also be arranged in a different manner. For example, execution of a software application may be carried out entirely in one user device like  1250 ,  1251  or  1260 , or in one server device  1240 ,  1241 , or  1242 , or across multiple user devices  1250 ,  1251 ,  1260 , or across multiple network devices  1240 ,  1241 , or  1242 , or across both user devices  1250 ,  1251 ,  1260  and network devices  1240 ,  1241 , or  1242 . For example, the capturing of user input through a user interface may happen in a first device, the data processing and providing information to the user may happen in a second (different) device, and the co-occurrence data processing subsystem  400  may reside in a third device. Application elements and libraries may be implemented as software components residing on one device. Alternatively, the software components may be distributed across several devices. The software components may be distributed across several devices so as to form a cloud. 
     A user device  1250 ,  1251  or  1260  may also act as web service server, just like the various network devices  1240 ,  1241  and  1242 . The functions of this web service server may be distributed across multiple devices, too. 
       FIG. 12   b  shows a server  1240 , which comprises a memory  1245 , one or more processors  1246 ,  1247 , and computer program code  1248  residing in the memory  1245  for implementing, for example, the functionalities of a software application like a social media service. Servers  1240 ,  1241 ,  1242  shown in  FIG. 11  may comprise these elements for employing functionality relevant to each server. 
     The different embodiments may be implemented as software running on mobile devices and optionally on devices offering network-based services. 
     The mobile devices may be equipped at least with a memory or multiple memories, one or more processors, display, keypad, motion detector hardware, and communication means such as 2G, 3G, WLAN, or other. The different devices may have hardware like a touch screen (single-touch or multi-touch) and means for positioning like network positioning or a global positioning system (GPS) module. There may be various applications on the devices such as a calendar application, a contacts application, a map application, a messaging application, a browser application, a gallery application, a video player application and various other applications for office and/or private use. 
     The system  500  may be configured to carry out various tasks. Program code may be run in the system in order to carry out the tasks. These tasks may include e.g. creation of text, receiving and sending messages, playing music, capturing video, receiving news, receiving weather information, updating and viewing a calendar, browsing in the internet, and/or navigating in the streets of a city, etc. The system may further comprise one or more functional (physical) units to carry out the tasks. As the functional units, the system may comprise e.g. a video camera, a microphone, an audio reproduction unit, a display screen, an image projector, a radio frequency communication unit (WLAN, Bluetooth, NFC), a unit capable of communicating with a mobile communications network, a GPS navigation unit etc. 
     Words for the bags may obtained e.g. from one or more sensors G 1 . The sensors may include e.g. an acceleration sensor, a location sensor, a microphone, a radio receiver, an illumination sensor, a camera, an infrared radiation sensor, temperature sensor, air pressure sensor, magnetic compass. 
     A user device may be powered by a rechargeable battery. For example the user device may be carried by a traveling user such that the battery of the user device can be charged only occasionally (i.e. not at any time). Collected co-occurrence data may e.g. reveal in which kind of situations energy-consuming functionalities are typically activated by the user. Collected co-occurrence data may e.g. reveal when a possibility of recharging the battery is typically available. 
     In an embodiment, a battery operated system may be charged occasionally e.g. from an unreliable mains power network, from a local generator, from a solar cell and/or from a wind turbine. Co-occurrence data may reveal e.g. in which kind of situations energy-consuming functionalities are typically activated. Co-occurrence data may reveal how the availability of energy typically depends e.g. on the time (e.g. day or night), season (winter or summer), weather conditions (wind, non wind, sunlight, not sunlight). Co-occurrence data may reveal when a failure of the mains power network has typically happened. 
     The system  500  may comprise an uninterruptible power supply (UPS). In case of a power failure, unnecessary functionalities may be switched off based on predictions provided by the subsystem  400 . 
     The word may be a string. The word may be a number. The word may comprise a sequence comprising letters and/or numbers. The word may comprise a sequence of ASCII codes represented in binary, decimal or hexadecimal format. The word may have a semantic meaning, but this is not necessary. The word may also be a uniform resource identifier (URI) such as a uniform resource name (URN) or a uniform resource locator (URL). The word may be an abbreviation or an acronym. The “words” may also be called as “tags”. 
     The co-occurrence data is gathered to the experience matrix EX by using groups of words called as bags. A bag of words may also be called as a group of words or as a set of words. 
     A prediction can be made by using co-occurrence data stored in the experience matrix EX 1 . The “prediction” may also comprise determining a word representing a present event or a past event, i.e. it does not necessarily refer to a future event. The prediction may mean estimating the most probable word or words describing a situation. 
     The length of the vectors of the experience matrix EX 1  does not need to be increased even when data is gathered from a high number of bags. In an embodiment, an experience matrix EX 1  may comprise co-occurrence data gathered from N BG  bags such that the number N BG  of the bags (i.e. “documents”) is substantially higher than the number m of columns of the experience matrix EX 1 . 
     The “context” of a word may mean a verbal environment of said word such that said word (itself) is excluded from said environment. In this sense, a word does not belong to its own context. 
     The vectors of the experience matrix EX 1  and the query vector QV1 may comprise information about the verbal environment of one or more words. The vectors of the experience matrix EX 1  may also be called as context vectors. The query vector QV1 may also be called as a context vector. 
     In general, entries of the vocabulary VOC1 may be strings containing one or more symbols. 
     In an embodiment, entries of the vocabulary VOC1 may be numbers instead of being natural language words. Entries of an auxiliary table may be natural language words, and the auxiliary table may contain pointers to the numbers of the vocabulary VOC1. A word of natural language may be mapped to a number by using the auxiliary table. A number may be mapped to a word of natural language by using the auxiliary table. The auxiliary table may be called e.g. as a natural language dictionary. In particular, the auxiliary table may be a multilingual dictionary containing words of several different natural languages. A first word of a first natural language and a second word of a second natural language may be associated with the same entry of the vocabulary VOC1 by using the multilingual dictionary. A first word of a first natural language and a second word of a second natural language may be associated with the same number of the vocabulary VOC1 by using the multilingual dictionary. The multilingual dictionary may comprise e.g. an English-to-number dictionary, a Finnish-to-number dictionary and/or a German-to-number dictionary. Thus, the same vocabulary VOC1, the same basic matrix RM1 and/or the same experience matrix EX 1  may be used with English, Finnish and/or German words. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 An example of a dictionary for associating words 
               
               
                 of one or more natural languages with numbers. 
               
            
           
           
               
               
               
               
               
            
               
                   
                 1st Language 
                 2nd language 
                 3rd language 
                 number 
               
               
                   
                   
               
               
                   
                 dog 
                 koira 
                 hund 
                 23624521 
               
               
                   
                 cat 
                 kissa 
                 katze 
                 63245234 
               
               
                   
                 meeting 
                 kokous 
                 versammlung 
                 43254323 
               
               
                   
                   
               
            
           
         
       
     
     The words on the rows 2 to 4 of this table are not to be translated during proceedings of this patent or patent application. 
     Thus, the system  500  may handle multilingual information. The system  500  may gather information from several different states e.g. via the Internet. The resulting experience matrix EX 1  may be language-independent. The same experience matrix EX 1  may be used globally. 
     A subsystem  400  may comprise an interface ( 501 ) for receiving a word (W 3 ) for a bag (BAG1). The subsystem  400  may be implemented in a single device. A sparse vector supply (SUP1) and/or a combining unit (LCU1) and/or a control unit (CNT1) of the subsystem  400  may be configured to associate words (W1, W2) with the sparse vectors (a 1 ,a 2 ) by using the vocabulary (VOC1). The sparse vector supply (SUP1) and/or the combining unit (LCU1) and/or the control unit (CNT1) may be configured to ignore a word, which is not contained in the vocabulary (VOC1). The sparse vector supply (SUP1) and/or the combining unit (LCU1) and/or the control unit (CNT1) is configured to add a further word to the vocabulary (VOC1) when the further word is a system word, a uniform resource locator (URL), or a word classified to be a vocabulary word. 
     One or more of the functionalities of a system  500  may be carried out by a control unit CNT1. One or more of the functionalities of a subsystem  400  may be carried out by a control unit CNT1. One or more of the functionalities of a device may be carried out by a control unit CNT1. The collector (WRU1), the sparse vector supply (SUP1), the combiner or combiners (LCU1, LCU2), the difference analysis unit (DAU1) may be partly or completely implemented by a control unit CNT1. A device (e.g. the device  1251  shown in  FIGS. 11 and 12   a ) of a system  500 , in particular a control unit CNT1 of the device may be configured to control the device and/or the system based on a prediction OUT1. The device, in particular a control unit CNT1 of the device may be configured to control a user interface  501  based on the prediction OUT1. The device, in particular a control unit CNT1 of the device may be configured to present a menu (B1,B2) based on the prediction OUT1 (See e.g.  FIGS. 8   b  and  8   c ). The device, in particular a control unit CNT1 of the device may be configured to determine an auxiliary query word T6 from a first word W 1 ,T1 by using a calendar, dictionary, electronic map, or tokenizing (See  FIGS. 10   a  and  10   b ). The first device may comprise the memory MEM2. The device, in particular a control unit CNT1 of the device may be configured to use the prediction OUT1 as an input word of a browser or as an input for a social network service. The device, in particular a control unit CNT1 of the device may be configured to associate a word of a first natural language and a different word of a second natural language with the same vector (e.g. v k ) of the matrix EX 1  by using a multilingual dictionary. The device, in particular a control unit CNT1 of the device may be configured to determine a query word (Q1) based on an environmental condition detected by a sensor (NAV1, G 1 ). The device, in particular a control unit CNT1 of the device may be configured to associate query words (Q 1 ,Q 2 ) with the vectors of the matrix (EX 1 ) by using a vocabulary (VOC1). 
     The system  500  or a first device of the system  500  may comprise an interface for copying vectors of the experience matrix EX 1  from a memory of a second device to the memory MEM2. A first device (e.g. the device  1251 ) may comprise an interface for copying vectors of the experience matrix EX 1  from a memory of a second device (e.g.  1240 ) to a memory (MEM2) of a said device ( 1251 ). 
     For the person skilled in the art, it will be clear that modifications and variations of the devices according to the present invention are perceivable. The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.