Abstract:
A method and apparatus for creating data carousels including representing an object carousel in XML according to a predefined XML schema, analyzing the XML representation of the object carousel with regard to technical standards for data carousels and broadcast systems, creating a representation of a data carousel in XML according to a predefined XML schema and based on the step of analyzing and providing data to a carousel according to the XML representation of the data carousel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for creating data carousels, in particular providing a user who has a particular file structure in mind with an easy mechanism by which to create and optimise appropriate data carousels. 
     2. Description of the Related Art 
     A data carousel may be created by developing new data or editing existing data. 
     For instance as part of a DVB compliant system, it is known to provide an information server for broadcasting any form of data, such as MHEG5 applications, HTML pages, Java applications, IRD software upgrades and other data services in the form of DSMCC objects on data carousels. An IRD is an Integrated Receiver Decoder and this term is used in standards documents to describe devices capable of receiving and decoding digital streams, eg. set top boxes and integrated digital TV sets. 
     Raw data may be divided into appropriate DSI (Download Server Initiate), DII (Download Information Indication) or DDB (Download Data Block) sections for insertion into MPEG transport stream packets as a data carousel. These are three types of messages defined in DSM-CC that carry the structure of a data carousel in the broadcast stream. In fact, DSI, DII and DDB are “messages” but “DSI section” is used to describe a MPEG section carrying a DSI message. Sections are split into packets, the lowest level structure in the stream. A data carousel is the collection of DSI, DII and DDB messages. 
     Alternatively, however, a user may determine a desired file structure for an object carousel consisting of files, directories and other object types. In DSM-CC there are five object types in an object carousel, namely Files, Directories, a Service Gateway, Streams and StreamEvents. These can all exist in the hierarchical structure that is like a filesystem. It is then a non trivial matter to rearrange the data of the object carousel into DSI, DII and DDB sections in an optimised manner for broadcast as a data carousel. There are many possible data carousel structures that can represent a given object carousel. It is desirable to choose an optimal data carousel that will be most effective by using knowledge of the intended use for the files in the object carousel and knowledge of the receiving equipment, but some experimentation is required to achieve this optimisation. Each time the user wishes to make alterations to the file structure on which the object carousel is based, it is necessary to reconsider entirely the structure of the corresponding data carousel. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a method and apparatus by which a user can easily create data carousels corresponding to desired file structures or object carousels. Furthermore, it is an object to provide a system whereby a user may more easily optimise data for use with a data carousel. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a method of creating data carousels including representing an object carousel in a structured data format, analysing the structured data format representation of the object carousel for compatibility with at least one predetermined technical standard, creating a representation of a data carousel in the structured data format based on the step of analysing and providing output data to a carousel according to the structured data format representation of the data carousel. 
     According to the present invention, there is also provided an apparatus for creating data carousels, including a memory containing a data format definition for representing object carousels in a structured data format, a memory containing a data format definition for representing data carousels in the structured data format, a GUI by which a user may create a representation of an object carousel in the structured data format, a processor for analysing the structured data format representation of the object carousel for compatibility with at least one predetermined technical standard and for creating, on the basis of the analysis, a representation in the structured data format of a data carousel according to the data format definition for the structured data format representing data carousels. 
     In this way, by defining the required object carousel as a structured data format representation, it is possible to provide a predetermined algorithm in any appropriate processing language to automatically form a structured data format representation of an equivalent data carousel. Furthermore, compared to previous binary representations of the data carousel, the structured data format representation allows a user relatively easily to understand the structure of the data carousel. This allows the user to edit the resulting data carousel and to optimise it with regard to its use in providing an output byte stream suitable for broadcast. 
     In order to allow conversion from the object carousel structured data format representation to the data carousel structured data format representation, the two structured data format representations should follow predetermined formats. Hence, respective data format definitions may be defined for the structured data format representing object carousels and the structured data format representing data carousels. 
     Once provided with the data format definition for the structured data format representing object carousels, a user may construct a desired data structure in the structured data format for the object carousel. This may then be converted automatically to structured data conforming to the data format definition for the structured data format representing data carousels. With the data format definition for structured data representing data carousels, the user may then edit the structured data representation of the data carousel so as to optimise it. 
     In this respect, the apparatus may be provided with a GUI allowing a user to edit the structured data format representation of the data carousel so as to optimise the arrangement of the data for use as part of a carousel. 
     Having prepared an appropriate data carousel with the structured data format representation, an output stream may be provided to a carousel. Hence, the apparatus preferably includes an output processor for providing data to a carousel according to the structured data format representation of the data carousel. 
     It will be understood that the data carousel represented by the structured data format representation must conform to the appropriate technical standards for the system in which the data carousel is to be broadcast. 
     The specific examples described below are based on several standards documents published by various international organisations. 
     ISO publish the MPEG-2 family of standards of which part 1 (Systems) defines transport streams, packets, sections and multiplexing and part 6 (DSM-CC) defines underlying object and data carousel structures. 
     There are other standards which govern individual digital TV systems such as MHEG-5 (published by ISO) and MHP (published by DVB). They mainly define how the receiving equipment operates but they also refer to the MPEG standards and define further refinements and constraints on the stream structures that are generated. 
     Hence, the technical standards include appropriate standards for carousels and broadcast systems. Preferably, they include DSM-CC standards and relevant standards for broadcast systems. 
     Preferably, the structured data format is XML such that the data format definitions are XML schemas. 
     As mentioned above, conversion from the XML representation of the object carousel to the XML representation of the data carousel can be conducted in any appropriate manner as a data transformation. However, it is particularly advantageous to use an XSLT algorithm to carry out this conversion, since this is particularly well suited. The XSLT language allows convenient interpretation and manipulation of data in XML format. 
     It should be noted that converting the XML representation of the object carousel with an XSLT algorithm is not straightforward, since the XSLT algorithm will require knowledge of the sizes of the files of the object carousel in order to create the appropriate XML representation of the data carousel. Hence, preferably, the sizes of the files of the object carousel are determined and provided in XML as a look-up table such that the XSLT algorithm uses the look up table when creating the XML representation of the data carousel. 
     It will be appreciated that the present invention and its preferred features as described above can be embodied as a computer program or code components stored on a computer readable storage medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a generalized broadcast system; 
         FIG. 2  illustrates information servers for producing data carousels; 
         FIG. 3  illustrates schematically object/data carousel; 
         FIG. 4  illustrates schematically a file structure in relation to a data carousel structure; 
         FIG. 5  illustrates schematically conversion from object to data carousels; 
         FIG. 6  illustrates schematically an apparatus for embodying the present invention; and 
         FIG. 7  illustrates schematically conversion from object to data carousels. 
     
    
    
       FIG. 1  illustrates a broadcasting system, such as a DVB system, in which an information server is incorporated for providing various types of data file on a carousel. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be more clearly understood from the following description, given by way of example only, with reference to the accompanying drawings. 
     A play-out section  2  incorporates a number of video/audio sources  4  as well as live sources  6 . Data from these sources, for instance in the form of MPEG-2 transport stream packets, is fed to a multiplexer  8  and output from the play-out section  2 . The multiplexed stream of data is fed to a modulator  10  for transmission, in this example, from a satellite  12 . The signal is then received by an IRD such as set top box  14  of television  16 . Signals from a number of other modulators  10 ′,  10 ″, etc may be fed together and transmitted to the satellite  12 . 
     In this system, it is also possible to provide an information server  18 . Just like the video/audio sources  4 , 6 , the information server  18  provides data, for instance in the form of MPEG transport stream packets to the multiplexer  8  for insertion into the data stream for transmission. The information server may be used to broadcast any form of data, but, in particular, MHEG5 applications, HTML pages, Java applications, IRD software upgrades and other data services in the form of DSM-CC objects on data carousels. 
     The information server may be controlled by a host computer  20 . 
     The arrangement of data on object or data carousels is well known in the art and, indeed, has to conform to certain standards, according to the systems in question. 
       FIG. 2  illustrates how one host computer may be used to control any number of information servers, each producing a number of streams. 
     The host, together with an information server constructs a carousel of information, for instance as illustrated in  FIG. 3 . Transport stream data is constructed appropriately for transmitting in rotation a series of files, directories and other objects. For instance, each page as illustrated in  FIG. 3  might comprise MHEG or HTML files or Java applications. As a result, the stream produced includes each of those pages in turn. 
     As illustrated, it is also possible to construct sub carousels, such that on each rotation of the main carousel of pages, a particular page itself rotates through a series of sub pages. 
     As is well known, the output stream is arranged in a predetermined manner. For instance, for DSM-CC, appropriate DSI, DII or DDB sections are arranged and assembled in MPEG transport stream packets. 
     As illustrated schematically in  FIG. 4 , the DSI/DII/DDB sections may be constructed using raw data  28 . Often, however, a user prepares files  30  and determines a required file structure for an object carousel. This must then be converted to the appropriate DSI/DII/DDB sections. 
     Conversion of the various files  30  and their linked inter relations into the appropriate sections is a non trivial process. It is particularly difficult to provide sections in an optimised manner for broadcast and for efficient use by the receiving equipment. A large part of the optimisation process is delivering the data in a way that the receiving equipment can load it quickly from the stream in the order that it needs. 
     As illustrated in  FIG. 5 , it is proposed that the file structure of the object carousel should be created as an XML representation. XML stands for Extensible Mark-up Language and is a general purpose language that can be used to represent any type of structured information. As illustrated in  FIG. 6 , a GUI (Graphical User Interface)  40  interacts with a processor  42 , for instance including a memory, to enable a user to create the desired object carousel and XML representation  50 . Once the desired object carousel has been created as the XML representation  50 , the processor  42  then conducts a predetermined conversion so as to produce an XML representation  52  of an equivalent data carousel. At this point, the processor  42  may be used to control an output processor  44  to create the required data stream on the basis of the data carousel defined by the XML representation. In particular, the output processor  44  derives the required raw data, for instance from some storage means and arranges this into appropriate sections as defined by the XML representation of the data carousel. 
     In this way, a user easily achieves an appropriate data carousel according to his/her requirements as defined for the object carousel. Furthermore, the XML representation of the data carousel may be relatively easily understood by the user, particularly as compared to bit/byte representations of data carousels. By means of the GUI  40 , the user is then able to modify the generated data carousel as required by modifying the XML representation  52 . In comparison, making equivalent modifications of a bit/byte data carousel would be extremely difficult if not impossible for most users. 
     The transformation or conversion process preferably includes the following steps. 
     The object carousel root directory, file, directory and other object declarations are mapped directly into the data carousel document, since the declaration format is identical for object and data carousels. 
     The object carousel contains a sequence that lists the files, directories and other objects that are to appear in the carousel. A list of modules is defined by working sequentially through the object carousel sequence. A module is “packed” with each object in order up to the point where adding another object would make the cumulative value of the object sizes exceed the module size limit defined in the DSM-CC specification or other standards for broadcast systems as appropriate. A new module is then created until the sequence is fully completed. This algorithm makes a simple fit that can be further optimised by hand later. 
     A message sequence is defined with the DSI and DII messages at the beginning referring to the modules in a simple linear sequence. 
     As the module declarations contain objects in the order described in the object carousel sequence, a message sequence is defined where each module is simply listed in order. 
     The transformation algorithm is representative of methods used by DSM-CC carousel servers to generate a transport stream. The object to data carousel mechanism allows a user to fine-tune the resulting data carousel before generation of a transport stream to ensure better performance based on the rough hints from the transformed object carousel. The object-data carousel transformation mechanism also allows algorithm designers to create alternative mappings to form the basis of later hand optimisation. As a tool, the translation mechanism provides an effort saving measure that can yield considerable benefits. 
     In order to allow a predetermined conversion algorithm to be used, the formats of the XML representations for the object and data carousels are predetermined. This may be achieved by appropriate respective XML schemas. 
     The following is an example of the XML schema for the object carousel representation.
         -&lt;xsd:schema xmlns:xsd=“http://www.w3.org/2001/XMLSchema”&gt;   -&lt;xsd:annotation&gt;   &lt;xsd:documentation&gt;Carousel Configuration schema for Sony MediaCaster&lt;/xsd:documentation&gt;   &lt;/xsd:annotation&gt;   -&lt;!-- elements --&gt;   &lt;xsd:element name=“carousel” type=“carouselType” /&gt;   &lt;xsd:element name=“root” type=“directoryType” /&gt;   &lt;xsd:element name=“directory” type=“directoryType” /&gt;   &lt;xsd:element name=“file” type=“fileType” /&gt;   &lt;xsd:element name=“cycle” type=“cycleType” /&gt;   &lt;xsd:element name=“instance” type=“instanceType” /&gt;   &lt;xsd:element name=“stream” type=“streamType” /&gt;   &lt;xsd:element name=“streamEvent” type=“streamEventType” /&gt;   &lt;xsd:element name=“objectSequence” type=“objectSequenceType” /&gt;   &lt;xsd:element name=“objectRef” type=“objectRefType” /&gt;   &lt;xsd:element name=“comment” type=“xsd:string” /&gt;   -&lt;!-- types --&gt;   -&lt;xsd:complexType name=“carouselType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref=“root” /&gt;   &lt;xsd:element ref=“objectSequence” /&gt;   &lt;/xsd:sequence&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“objectSequenceType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref=“objectRef” minOccurs=“0” maxOccurs=“unbounded” /&gt;   &lt;/xsd:sequence&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“directoryType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   -&lt;xsd:choice minOccurs=“0” maxOccurs=“unbounded”&gt;   &lt;xsd:element ref=“file” /&gt;   &lt;xsd:element ref=“cycle” /&gt;   &lt;xsd:element ref=“directory” /&gt;   &lt;/xsd:choice&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“fileType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“content” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“immediate” type=“xsd:boolean” use=“required” /&gt;   &lt;xsd:attribute name=“contentType” type=“xsd:string” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“cycleType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref=“instance” maxOccurs=“unbounded” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“instanceType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“content” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“contentType” type=“xsd:string” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   &lt;xsd:complexType name=“streamType” abstract=“true”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   &lt;xsd:complexType name=“streamEventType” abstract=“true”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“objectRefType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“path” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   &lt;/xsd:schema&gt;       

     As exemplified above, a preferred schema allows concise declaration of the hierarchical structure of files, directories and other objects in an object carousel, together with hints about the order in which they should appear in a data carousel. 
     An example of an appropriate XML schema for the data carousel representation is given below.
         -&lt;xsd:schema xmlns:xsd=“http://www.w3.org/2001/XMLSchema”&gt;   -&lt;xsd:annotation&gt;   &lt;xsd:documentation&gt;Carousel Configuration schema for Sony MediaCaster&lt;/xsd:documentation&gt;   &lt;/xsd:annotation&gt;   -&lt;!-- elements --&gt;   &lt;xsd:element name=“carousel” type=“carouselType” /&gt;   &lt;xsd:element name=“root” type=“directoryType” /&gt;   &lt;xsd:element name=“directory” type=“directoryType” /&gt;   &lt;xsd:element name=“file” type=“fileType” /&gt;   &lt;xsd:element name=“cycle” type=“cycleType” /&gt;   &lt;xsd:element name=“instance” type=“instanceType” /&gt;   &lt;xsd:element name=“stream” type=“streamType” /&gt;   &lt;xsd:element name=“streamEvent” type=“streamEventType” /&gt;   &lt;xsd:element name=“programStreamInfo” type=“programStreamInfoType” /&gt;   &lt;xsd:element name=“eventStreamInfo” type=“eventStreamInfoType” /&gt;   &lt;xsd:element name=“event” type=“eventType” /&gt;   &lt;xsd:element name=“module” type=“moduleType” /&gt;   &lt;xsd:element name=“objectRef” type=“objectRefType” /&gt;   &gt;xsd:element name=“binaryContent” type=“binaryContentType” /&gt;   &lt;xsd:element name=“DII” type=“DIIType” /&gt;   &lt;xsd:element name=“moduleInfo” type=“moduleInfoType” /&gt;   &lt;xsd:element name=“tapList” type=“tapListType” /&gt;   &lt;xsd:element name=“privateData” type=“privateDataType” /&gt;   &lt;xsd:element name=“objectUseTap” type=“objectUseTapType” /&gt;   &lt;xsd:element name=“tap” type=“tapType” /&gt;   &lt;xsd:element name=“userInfo” type=“userInfoType” /&gt;   &lt;xsd:element name=“labelDescriptor” type=“labelDescriptorType” /&gt;   &lt;xsd:element name=“cachingPriorityDescriptor”   type=“cachingPriorityDescriptorType” /&gt;   &lt;xsd:element name=“descriptor” type=“descriptorType” /&gt;   &lt;xsd:element name=“DSI” type=“DSIType” /&gt;   &lt;xsd:element name=“messageSequence” type=“messageSequenceType” /&gt;   &lt;xsd:element name=“messageRef” type=“messageRefType” /&gt;   &lt;xsd:element name=“elementaryStream” type=“elementaryStreamType” /&gt;   &lt;xsd:element name=“comment” type=“xsd:string” /&gt;   &lt;!-- types --&gt;   -&lt;xsd:complexType name=“carouselType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref=“root” /&gt;   &lt;xsd:element ref=“module” maxOccurs=“unbounded” /&gt;   &lt;xsd:element ref=“DII” maxOccurs=“unbounded” /&gt;   &lt;xsd:element ref=“DSI” /&gt;   &lt;xsd:element ref-“messageSequence” /&gt;   &lt;xsd:element ref=“elementaryStream” /&gt;   &lt;/xsd:sequence&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“directoryType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   -&lt;xsd:choice minOccurs=“0” maxOccurs=“unbounded”&gt;   &lt;xsd:element ref=“file” /&gt;   &lt;xsd:element ref=“cycle” /&gt;   &lt;xsd:element ref=“directory” /&gt;   &lt;xsd:element ref=“stream” /&gt;   &lt;xsd:element ref=“streamEvent” /&gt;   &lt;/xsd:choice&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“fileType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“content” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“immediate” type=“xsd:boolean” use=“required” /&gt;   &lt;xsd:attribute name=“contentType” type=“xsd:string” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   &lt;xsd:complexType name=“cycleType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref=“instance” maxOccurs=“unbounded” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“instanceType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“content” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“contentType” type=“xsd:string” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“streamType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref-“programStreamInfo” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“streamEventType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref=“event” maxOccurs=“unbounded” /&gt;   &lt;xsd:element ref=“eventStreamInfo” /&gt;   &lt;xsd:element ref=“programStreamInfo” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“programStreamInfoType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“audio” type=“xsd:boolean” use=“required” /&gt;   &lt;xsd:attribute name=“video” type=“xsd:boolean” use=“required” /&gt;   &lt;xsd:attribute name=“data” type=“xsd:boolean” use=“required” /&gt;   &lt;xsd:attribute name=“description” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“durationSeconds” type=“xsd:integer” use=“required” /&gt;   &lt;xsd:attribute name=“durationMicroSeconds” type=“xsd:integer” use=“required” /&gt;   &lt;xsd:attribute name=“transportStreamID” type=“xsd:integer” use=“required” /&gt;   &lt;xsd:attribute name=“programNumber” type=“xsd:integer” use=“required” /&gt;   &lt;xsd:attribute name=“networkID” type=“xsd:integer” use=“required” /&gt;   &lt;xsd:attribute name=“PMTTag” type=“xsd:integer” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   &lt;xsd:complexType name=“eventStreamInfoType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“pid” type=“xsd:integer” use=“required” /&gt;   &lt;xsd:attribute name=“bitrate” type=“xsd:integer” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“eventType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“id” type=“xsd:integer” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“moduleType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   -&lt;xsd:choice&gt;   &lt;xsd:element ref-“objectRef” minOccurs=“0” maxOccurs=“unbounded” /&gt;   &lt;xsd:element ref=“binaryContent” /&gt;   &lt;/xsd:choice&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“objectRefType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“path” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   &lt;xsd:complexType name=“binaryContentType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“path” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“DIIType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“moduleInfo” minOccurs=“0” maxOccurs=“unbounded” /&gt;   &lt;xsd:element ref=“privateData” minOccurs=“0” maxOccurs=“unbounded” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“transactionID” type=“xsd:hexBinary” /&gt;   &lt;xsd:attribute name=“downloadID” type=“xsd:integer” /&gt;   /xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“moduleInfoType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“tapList” /&gt;   &lt;xsd:element ref=“userInfo” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“moduleRef” type=“xsd:string” use=“required” /&gt;   &lt;xsd:attribute name=“moduleTimeOut” type=“xsd:hexBinary” /&gt;   &lt;xsd:attribute name=“blockTimeOut” type=“xsd:hexBinary” /&gt;   &lt;xsd:attribute name=“minBlockTime” type=“xsd:hexBinary” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“tapListType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“objectUseTap” /&gt;   &lt;xsd:element ref=“tap” minOccurs=“0” maxOccurs=“unbounded” /&gt;   &lt;/xsd:sequence&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“objectUseTapType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“tag” type=“xsd:integer” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“tapType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“id” type=“xsd:integer” /&gt;   &lt;xsd:attribute name=“use” type=“xsd:integer” /&gt;   &lt;xsd:attribute name=“tag” type=“xsd:integer” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“userInfoType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element name=“compressedModuleDescriptor” /&gt;   &lt;xsd:element ref=“labelDescriptor” /&gt;   &lt;xsd:element ref=“cachingPriorityDescriptor” /&gt;   &lt;xsd:element ref-“descriptor” maxOccurs=“unbounded” /&gt;   &lt;/xsd:sequence&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“labelDescriptorType”&gt;   &lt;xsd:sequence/&gt;   &lt;xsd:attribute name=“label” type=“xsd:string” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“cachingPriorityDescriptorType”&gt;   &lt;xsd:sequence/&gt;   &lt;xsd:attribute name=“priorityValue” type-“xsd:byte” /&gt;   &lt;xsd:attribute name=“transparencyLevel” type=“xsd:byte” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“descriptorType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“tag” type=“xsd:byte” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“privateDataType”&gt;   &lt;xsd:sequence /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“DSIType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“messageSequenceType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;xsd:element ref=“messageRef” minOccurs=“0” maxOccurs=“unbounded” /&gt;   &lt;/xsd:sequence&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“messageRefType”&gt;   &lt;xsd:sequence /&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   -&lt;xsd:complexType name=“elementaryStreamType”&gt;   -&lt;xsd:sequence&gt;   &lt;xsd:element ref=“comment” minOccurs=“0” /&gt;   &lt;/xsd:sequence&gt;   &lt;xsd:attribute name=“name” type=“xsd:string” use=“required” /&gt;   &lt;/xsd:complexType&gt;   -&lt;!-- --&gt;   &lt;/xsd:schema&gt;       

     As exemplified above, a preferred schema provides a readable description of the detailed structure of a data carousel. It specifies the grouping of objects into modules, the parameters associated with modules and the order and relative frequency of DSI, DII and DDB sections in the output stream. These are all factors that can affect the performance of the broadcast at the receiving equipment and it is desirable to allow easy experimentation with these parameters in order to maximise performance. 
     It will, of course, be evident that other schemas could also be constructed, though, then, of course, the conversion between the XML representations would be different. 
     Conversion may be achieved with any appropriate algorithm defined using any desired language, such as C++. 
       FIG. 7  illustrates schematically a conversion process using an XSLT algorithm  54 . XSLT stands for Extensible Stylesheet Language Transformation and is a language and processor that allows relatively easy development of transformations between different formats of XML. It is particularly well suited to converting XML, because the language has built-in features for interpreting and transforming XML. However, the XSLT algorithm needs to know the sizes of the files of the object carousel in order to create the appropriate data carousel XML representation. The XSLT algorithm itself is unable to determine the sizes. Therefore, an additional algorithm  56  is provided to analyse the object carousel so as to determine the size of files and provide this information as an XML look-up table  58 . Thus, the XSLT conversion algorithm analyses the XML representation of the object carousel and uses information regarding file size from the XML look-up table to create the XML representation of the data carousel. 
     The stylesheet implements a simple module packing algorithm to transform an XML object carousel structure into a detailed XML data carousel structure. Implementation in XSLT allows convenient interpretation of the incoming XML structure and also allows flexibility about where in the system the algorithm is executed. 
     In addition, more sophisticated techniques for creating data carousel structures would be relatively easy to incorporate and the implementation would be easily adaptable to accommodate future changes to the object carousel and data carousel XML schemas. 
     The look-up table algorithm for object carousel file sizes may be implemented as a UNIX shell script. An example is given below.
         #!/bin/sh   #   # Given an object carousel XML description on stdin, generate a list of   # Pathnames used by the carousel and the sizes of the corresponding   # files. The list is in XML and appears on stdout.   #   # usage: generateFileSizes carouselDir   #   # check args   if [$#!=1]; then
           echo “usage: generateFileSizes carouselDir”1&gt;&amp;2   exit 1   
           fi   # temporary file   TMPFILE=generateFileSizes.$$   # where are the carousel files?   CAROUSELDIR=“$1”   # separate elements that are on the same line   # NOTE it seems to be necessary to go via a temporary file . . .   # a pipe doesn&#39;t seem to work   sed -e′s/&gt;/&gt;Vg′&gt;$TMPFILE   # isolate the content files that appear in the carousel   FILES=‘cat $TMPFILE|sed -n -e’s/^.*content=\“\([^”]*\)\“.*$Λ1/p”   # output an element listing the files and their sizes   echo “&lt;files&gt;”   for i in $FILES; do   # get the size of a file   SIZE=‘1s -1 $CAROUSELDIR/$i|awk‘{print $5}’’   # output an element   echo “&lt;file path=\”$i\“size=\”$SIZE\“/&gt;”   done   echo “&lt;/files&gt;”   rm $TMPFILE       

     This script generates an XML look-up table that maps file names used by an object carousel to the sizes of the files. References to files are extracted from an XML object carousel description and each file is examined in turn to produce a list of XML elements, each containing the name of a file and its size in bytes. 
     The following is an example of a look-up table:
         &lt;files&gt;   &lt;file path=“diddle.txt” size=“168”/&gt;   &lt;file path=“dingdong.txt” size=“269”/&gt;   &lt;file path=“kxmrain.txt” size=“423”/&gt;   &lt;file path=“raining.txt” size=“212”/&gt;   &lt;file path=“Jack/jack.txt” size=“72”/&gt;   &lt;file path=“Jack/jacksprat.txt” size=“124”/&gt;   &lt;file path=“Jack/jackjill.txt” size=“259”/&gt;   &lt;file path=“More/sheep.txt” size=“167”/&gt;   &lt;file path=“More/owl.txt” size=“1205”/&gt;   &lt;file path=“More/Other/dance.txt” size=“194”/&gt;   &lt;file path=“More/Other/goosey.txt” size=“223”/&gt;   &lt;file path=“More/Other/hush.txt” size=“616”/&gt;   &lt;file path=“More/Other/kookaburra.txt” size=“299”/&gt;   &lt;file path=“More/Other/mulberry.txt” size=“1409”/&gt;   &lt;file path=“More/Other/unicom.txt” size=“222”/&gt;   &lt;file path=“More/Other/georgie.txt” size=“128”/&gt;   &lt;file path=“More/Other/hickory.txt” size=“125”/&gt;   &lt;file path=“More/Other/knickknack.txt” size=“2032”/&gt;   &lt;file path=“More/Other/ladybird.txt” size=“189”/&gt;   &lt;file path=“More/Other/spider.txt” size=“210”/&gt;   &lt;/files&gt;       

     Finally, it should be appreciated that the present invention is not constrained to television systems but could be applied to any data broadcast system, based, for instance, on MPEG streams, such as DAB (Digital Audio Broadcasting) digital radio or custom broadcast applications.