Abstract:
Described is a system and method for applying transforms to multi-part files. A request is received to access a stream within a multi-part file. Upon receipt of the request, a list of transforms associated with the stream is identified. The list is also included within the multi-part file. The transforms specified in the list of transforms are performed on data before completing the request. If the request is a write, the transforms encode the data. If the request is a read, the transforms decode the data. The list of transforms is order dependent. The list of transforms includes a data structure having a first stream that includes a map that correlates the stream with a name for the list of transforms. A second stream that lists each of the transforms for the stream. A third stream for each of the transforms listed that identifies information associated with the transform.

Description:
BACKGROUND OF THE INVENTION 
   Computer systems today typically store a large amount of data in several files. The format for the files may be one of several different formats that are compatible with various applications, such as word processors, spreadsheets, and the like. Many times it is necessary to transmit a file to another computer so that another user may see or manipulate the data within the file. Sometimes, when the file is quite large, a transformation (e.g., compression) is performed on the file before sending the file to the other computer. By compressing the file, less bandwidth is needed to send the data to the other computer. In other situations, another transformation (e.g., encryption) may be performed to protect the data from being seen by unauthorized users. 
   Some of these transformations have specific encoding methods and use a separate file (e.g., dictionary) to store information about the specific encoding method. The separate file must be used when accessing the transformed file. If the separate file becomes corrupted, lost, or otherwise unavailable, the transformed file becomes useless. In addition, because some of these transformations define their own specific encoding methods for interleaving encoded data and processing information, once the file is transformed, the file can not be shared or have common processing performed on it. In addition, before transforming a file, current transformations require that the data within the file to be arranged in contiguous bytes. Ensuring that the bytes for the file remain contiguous consumes a lot of overhead and is not viable for files that are edited quite often. Thus, while these transformations are very useful, the way in which they are implemented do not offer a versatile experience to users. 
   SUMMARY OF THE INVENTION 
   The present invention is directed at a system and method for implementing transformations that provide greater flexibility to users. Briefly stated, the present invention provides a mechanism for storing transformation information associated with one or more transformations within a multi-part file. The multi-part file also contains the data upon which the one or more transformations are applied. Thus, the present invention provides a file format for the multi-part file so that applications accessing the data may easily access the transformed data. In accordance with the invention, multiple data transforms may be chained together. These chained data transforms are referred to as a “data spaces”. Each data space has a unique order and type for the transforms that are chained together. For example, two data spaces may specify the same transforms, but specify a different order for applying the transforms. The transformation information contains information about the data spaces. 
   In accordance with another aspect of the invention, the multi-part file contains a plurality of streams. Each stream may be associated with one of the data spaces. Thus, in accordance with the present invention some streams within the multi-part file may be transformed while other streams may remain in their native format. This ability to transform specific streams without requiring transformation of the entire multi-part file offers great flexibility to users, such as allowing the user to encrypt only the sensitive information within the multi-part file (e.g., redacting documents). 
   Thus, the present invention is directed at a system and method for applying transforms to multi-part files. A request is received to access a stream within a multi-part file. Upon receipt of the request, a list of transforms associated with the stream is identified. The list is also included within the multi-part file. The transforms specified in the list of transforms are performed on data before completing the request. If the request is a write, the transforms encode the data. If the request is a read, the transforms decode the data. The list of transforms is order dependent. The list of transforms includes a data structure having a first stream that includes a map that correlates the stream with a name for the list of transforms. A second stream that lists each of the transforms for the stream. A third stream for each of the transforms listed that identifies information associated with the transform. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a functional block diagram that illustrates a computing device that may be used in implementations of the present invention. 
       FIG. 2  is a functional flow diagram generally illustrating an overview of a transformation process in accordance with the present invention. 
       FIG. 3  is a graphical representation of an exemplary tree hierarchy that represents the transform metadata shown in  FIG. 2 . 
       FIG. 4  is a graphical depiction of the transformation process. 
       FIG. 5  is a logical flow diagram generally illustrating a process for accessing transformed data within a multi-part file, in accordance with one embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The invention provides a mechanism for applying transforms to multi-part files. The mechanism provides a structure for specifying transformation information. The transformation information and the transformed data co-exist within the same document. The mechanism of the invention is preferably based on a multi-part file format that allows multiple types of streams within one document. The inventors have determined that the Object Linking and Embedding (OLE) compound file format is especially well suited to implementations of the invention. Thus, the following discussion describes the invention using the compound file format. However, those skilled in the art, after a careful reading of the following description, will recognize that other multi-file formats may implement the present invention with various modifications to the mechanism described below to accommodate the other multi-file formats. Thus, it will be appreciated that embodiments of the invention are not limited to those described here. 
   The invention will be described here first with reference to one example of an illustrative computing environment in which embodiments of the invention can be implemented. Next, a detailed example of one specific implementation of the invention will be described. Alternative implementations may also be included with respect to certain details of the specific implementation. 
   Illustrative Computing Environment of the Invention 
     FIG. 1  is a functional block diagram that illustrates a computing device that may be used in implementations of the present invention.  FIG. 1  illustrates an exemplary computing device that may be used in illustrative implementations of the present invention. With reference to  FIG. 1 , in a very basic configuration, computing device  100  typically includes at least one processing unit  102  and system memory  104 . Depending on the exact configuration and type of computing device  100 , system memory  104  may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. System memory  104  typically includes an operating system  105 , one or more program modules  106 , and may include program data  107 . Examples of program modules  106  include a browser application, a finance management application, a word processor, and the like. This basic configuration is illustrated in  FIG. 1  by those components within dashed line  108   
   Computing device  100  may have additional features or functionality. For example, computing device  100  may also include additional data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Such additional storage is illustrated in  FIG. 1  by removable storage  109  and non-removable storage  110 . Computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. System memory  104 , removable storage  109  and non-removable storage  110  are all examples of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by computing device  100 . Any such computer storage media may be part of device  100 . Computing device  100  may also have input device(s)  112  such as keyboard, mouse, pen, voice input device, touch input device, etc. Output device(s)  114  such as a display, speakers, printer, etc. may also be included. These devices are well know in the art and need not be discussed at length here. 
   Computing device  100  may also contain communication connections  116  that allow the device  100  to communicate with other computing devices  118 , such as over a network. Communication connections  116  are one example of communication media. Communication media may typically be embodied by computer readable instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave or other transport mechanism, and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. The term computer readable media as used herein includes both storage media and communication media. 
   General Discussion of Components 
     FIG. 2  is a functional flow diagram generally illustrating an overview of components of an environment implementing the present invention. Illustrated is a multi-part file  202 , preferably an OLE compound file. The OLE document model is known in the art and is widely recognized as a mechanism for containing many disparate types of data within a single document. Conventionally, the OLE compound file is used in conjunction with having several embedded files or other support content associated with a single document. Each element in the compound file is stored in a manner such that it can be manipulated by the application that created the element. Each element is stored as a stream, such as streams  204 ,  206 , and  208  shown in  FIG. 2 . As mentioned above, each stream may be one of several types. For instance, stream 1   204  may be a word processing document, stream 2   206  may be a spreadsheet, and streamZ  208  may be a graphics file. 
   In the past, upon requesting a transformation on the multi-part file  202 , the entire content of multi-part file  202  (i.e., streams  204 - 208 ) would have been required to be contiguous and would have been transformed together. However, in accordance with the present invention, the streams  204 - 208  need not be contiguous. Rather, the streams  204 - 208  may be sector-based. For the following discussion, sector-based files refer to files having multiple chunks of data that are stored and that represent the entire stream. The multiple chunks may be stored contiguously, but typically are stored non-contiguously. In one embodiment, the chunks may be fixed size, such a fixed at 512 bytes. Alternatively, the chunks may be variably sized without departing from the scope of the present invention. When the stream is edited, a new chunk of data may be created and stored in non-contiguous bytes in relations to the other chunks of data for the stream. Thus, sector-based files allow for easy editing of the stream without the overhead of ensuring that the stream remains contiguous. 
   As will be described in detail below, the present invention allows specified chunks of data  240  associated with a stream (e.g., stream  206 ) within the multi-part file  202  to be transformed without transforming other streams. Because the present invention allows specified streams to be transformed independent of other streams, the invention provides a great flexibility for securing and controlling data. For example,  FIG. 2  illustrates stream 2   206  undergoing a transformation process. Stream 2   206  may represents a spreadsheet containing the costs associated with a particular item. Therefore, it may be desirable to secure this cost information so that unauthorized users can not view the costs. Thus, the data  240  destined for stream 2   206  undergoes a chain of transforms (i.e., transforms  220 - 224 ). As one skilled in the art will appreciate, any number of transforms may be chained and may be chained in any order. The specific transforms that are chained and the order in which the transforms are chained represent a data space  230 . In general, a data space may specify one transform or may specify multiple transforms. In the above example, the last transform (e.g., transform  224 ) writes the transformed data to the stream 2   206 , which may reside on a disk (not shown). One embodiment for using the mechanism for applying transforms to multi-part files is described in detail in conjunction with  FIG. 4  below. 
   Discussion of a Particular Embodiment of the Invention 
     FIG. 3  is a graphical representation of one embodiment of a tree hierarchy that represents the transform metadata  210  shown in  FIG. 2 . In general, the tree hierarchy may be included within the multi-part file in any manner compatible with the multi-part file. The following discussion, describes the tree hierarchy with reference to compound files. In overview, compound files are commonly considered as a “file system within a file.” Within the compound file is a hierarchy of “storages,” which are analogous to directories in a file system, and “streams,” which are analogous to files in a file system. For  FIG. 3 , rectangular boxes represent the streams and ovals represent the storage. Before describing the transform metadata  210  of the present invention, one will note that the streams  204 - 208  (shown in  FIG. 2 ) are illustrated under the root  302  in this example hierarchy. Defining streams under the root is a common technique for compound file formats. 
   The transform metadata  210  provided by the present invention is now discussed in further detail. A special storage, named “\006DataSpaces”  310  off the root  302  stores the transform metadata  210 . The \006DataSpace storage  310  contains a DataSpaceMap stream  320 , a DataSpaceInfo storage  330 , and a TransformInfo storage  340 . For this embodiment, the name chosen for the special storage, “\006DataSpaces”, is written in context of the C Programming language. Thus, in this embodiment, the name begins with a single non-alphanumeric token and a token value of 6. In general, the name assigned to the special storage is arbitrary and depends on the user&#39;s implementation. 
   The DataSpaceMap stream  320  maps the streams (e.g., streams  204 - 208 ) with their associated data space. In one embodiment, the DataSpaceMap stream  320  is a table having two columns: a stream reference column  322  and a DataSpaceName column  324 . The contents within the stream reference column  322  refer to one of the streams (e.g., streams  204 - 208 ) stored within the compound document. The contents within the DataSpaceName refer to a specific data space that has been defined for the associated stream identified within the stream reference column  322 . One data space may be associated with any number of streams. For example, as shown in  FIG. 3 , the data space identified as “DataSpaceName 1 ” is associated with Stream 1   204  and Stream 2   206 . While the above description of the DataSpaceMap stream  320  describes the DataSpaceMap stream  320  as a table, those skilled in the art will appreciated that other data formats may also be used to identify and correlate the stream with a data space. 
   The DataSpaceInfo storage  330  contains one or more DataSpaceName streams (e.g., DataSpaceName stream  332  and  334 ). For the described embodiment, the DataSpaceName stream is named in accordance with standard, compound-file short name conventions. Each DataSpaceName stream  332  and  334  identifies a list  336  of transforms associated with the respective DataSpaceName stream  332  and  334 . In one embodiment, each of the DataSpaceName streams  332  and  334  may be an ordered list of the transforms that make up the data space. Because transforms stack, the order within the list  336  is important. In one embodiment, the first transform  337  within the list  336  is referred to as the “bottom” transform, which means the transform  337  is closest to the bits in the underlying data stream (e.g., stream  204 ). The last transform  339  within the list  336  is referred to as the “top” transform, which means the transform  339  is the closest to the consumer/producer of the data (e.g., an application). As will be described in detail below in conjunction with  FIG. 4 , the order specified in the list  336  determines the flow of data through the transforms. 
   The TransformInfo storage  340  contains one or more TransformInstance storages (e.g., TransformInstance storage  342 ,  344 , and  346 ). In one embodiment, the names of these substorages are the names of the transforms. Within each of the TransformInstance storages  342 ,  344 , and  346 , there is at least one stream named “\006Primary”  350 . The \006Primary stream  350  contains pertinent information about the specific transform, such as TransformClass Type  354  and TransformClass Name  356 . The TransformClass Type  354  denotes a particular transform class that implements a particular transform (e.g., LZ compression, Digital Rights Management (DRM) protection, and the like). In one embodiment, the TransformClass Name  356  is specified as a string that uniquely identifies the class (i.e., type) of the transform. The string that identifies the class may be a class name for the class that implements the transform. The TransformClass Type  354  specifies a type indicator that tells how to interpret the string specified in the TransformClass Name  356 . The \006Primary stream  350  may also contain space for TransformInstance Data  358 . The TransformInstanceData  358  stores information specified to the transform specified by the TransformClass Name  356  and TransformClass Type  354 . For example, if the transform is a compression transform, the TransformInstanceData  358  may contain a window size and the like. 
   For certain transforms, the TransformInstanceData  358  may not allow sufficient space to store the necessary information. Thus, as a further refinement, the present invention allows transforms to store additional information in a TransformInstanceData stream (e.g., TransformInstanceData stream  370 ). This is allowed as long as there are no name collisions with the \006Primary stream  350 . The nature of the TransformInstanceData will vary depending on the type of transform. 
   While the above tree hierarchy describes one embodiment of a document format for storing transformed data with its transformation information, those skilled in the art will appreciate that the hierarchy may be changed without impacting the operation of the present invention. Therefore, any tree hierarchy in which transformation information is stored along with the transformed data does not depart from the present invention.  FIG. 4  is a graphical depiction of the transformation process in which the mechanism for formatting documents having transformed data in accordance with the present invention is used. In this illustrative transformation process, an application  400  attempts to read and write to the multi-part file  202  described in  FIG. 2 . In general, each instance of a transform class takes an IStream interface as input, and outputs the encoded (i.e., transformed) data to another IStream interface. The transforms (e.g., transforms  420  and  422 ) have been registered and the data space associated with stream  206  as already been specified, such as via application programming interfaces provided by OLE compound documents. For example, when stream  206  was first created, the application that created the stream  206  within multi-part document  202  was responsible for specifying which transforms to apply to the data. This may have occurred via an argument list, where each argument referred to a transform. 
   The read and write access is via an OS layer. In the past, a write operation would have accessed stream 2   206  via IStream interface  414 . However, in accordance with the present invention, one or more transforms may be inserted before the IStream interface  414 . Each transform (e.g., transform  420  and  422 ) takes an IStream interface as input (IStream interface  410  and  412 , respectively), and output their encoded (i.e., transformed) data to another IStream interface (IStream interface  412  and  414 , respectively). 
   Likewise, when application  400  attempts to read stream 2   206  within multi-part file  202 , one or more inverse transforms (e.g., inverse transforms  450  and  452 ) may be inserted. The number of inverse transforms is identical to the number of transforms in order for the data to be properly decoded so that the application can understand the data. The manner in which the transforms are inserted between the application  400  and the stream  206  is now described in conjunction with  FIG. 5 . 
     FIG. 5  is a logical flow diagram generally illustrating a process for accessing transformed data within a compound file, in accordance with the invention. The process  500  begins at a starting block  501  where an application has requested an access to data within in stream of a multi-part file. The transform information  210  has already been specified for the stream. 
   At decision block, a determination is made whether the stream is a member of a data space. Referring to  FIG. 3 , for one embodiment, this determination is made by searching within the DataSpaceMap for the stream reference  322  that identifies the requested stream. If the stream reference  322  associated with the stream is not found, the stream does not have any transforms defined and processing proceeds to the end. In this situation, the application accesses the data in the way in which it was done before the present invention. However, if the stream reference  322  is contained within the DataSpaceMap, processing continues at block  504 . 
   At block  504 , the DataSpaceName associated with the stream reference  322  is obtained. The DataSpaceName may be a string or any other format. 
   At block  506 , using the DataSpaceName obtained from block  504 , the DataSpaceInfo storage is searched to identify the DataSpaceName stream associated with the DataSpaceName identified within the DataSpaceMap. The DataSpaceName stream contains a list of transforms associated with this data space name. 
   At block  508 , a transform from within the list is identified. Depending on whether the access is a write or a read, the transform may encode the data or may decode the data, respectively. The DataSpaceName stream lists each transform in a specific order. If the access is a write, the order is from top to bottom. If the access is a read, the order is from bottom to top. 
   At block  510 , the identified transform is applied. When applying the transform, the transform instance data is used to properly transform the data. If the access is a write, the transform (encode) is applied. If the access is a read, the inverse transform (decode) is applied. 
   At decision block  512 , a determination is made whether the data space includes any further chained transforms. This may be determined by seeing whether list  336  references any more transform instances. If the last transform in the data space has been applied, the last transform outputs the data and the process is complete. However, if there is another transform listed, processing loops back to block  508  and proceeds as described above until the last transform has been applied. 
   In addition, one skilled in the art will appreciate that the functionality provided by process  300  may be implemented in various ways. For example, there may be a mapping directly from the stream name to a transform list (skipping the use of a data space). Thus, the present invention includes this and other embodiments for mapping the stream to its transform information. Process  500  illustrates one such embodiment. 
   The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.