KR100898614B1 - Schema, syntactic analysis method and method of generating a bit stream based on a schema - Google Patents

Abstract

The present invention proposes a new type of schema derived from an XML schema that allows for describing the coding format in a comprehensive manner. Such a schema is used to generate a document representing a bit stream that is an instance of the schema or to parse the bit stream to generate a bit stream from a document representing the bit stream.

Coding Format, Schema, Bit Stream, Parsing

Description

Schema, syntactic analysis method and method of generating a bit stream based on a schema}

The present invention relates to a method for syntactically analyzing a bit stream comprising data having contents and structure according to a particular format, said method being intended to generate a tree-like representation of said stream. do. The invention is also a tree-like representation of the bit stream, which generates a bit stream in accordance with a particular format, using a particular import mode, from a document containing data, in particular imported data. It is about a method. The present invention also defines one or various data types that may have one or various facets, name, data type, nesting, order, and predefined or random occurrences. It includes a plurality of elements describing the number of, and the occurrence of the element relates to a schema, which is essential or optional.

The invention also provides a transmission system comprising at least one source entity and a destination entity, as well as a processing unit comprising computer programs for executing these methods and a storage means for storing such a schema and such computer programs. In which the source entity has such a schema and means for storing one or such programs.

The present invention has applications in the field of editing, modifying and merging content.

An example of an application of the invention is the adaptation of the contents to be sent to the destination as a function of the user profile (screen, computing capacity, storage capacity, link used for transmission, ...). Such an adaptation, in particular, allows to avoid sending useless data that is not available to the recipient, thus saving on passband.

In this regard, French Patent Application No. 0101530, filed on February 2, 2001, by Koninclike Philips Electronics N.V., generates a file with features from a basic document written in the mark-up language and is a basic progressive file. A method of generating a file has already been described, the method comprising a transformation step of generating a converted document by applying a predefined transformation, which is a function of the unique features, to a base document, File is generated from the converted document. This method consists of performing the necessary conversions on the base document with a structure of progressive files. This allows to avoid having to decode the basic progressive file in order to record the basic progressive file differently.

However, this file generation method implies the generation of a basic document describing the basic progressive file and then the generation of another file from the converted document.

It is an object of the present invention to propose an automatic and comprehensive method of performing these operations.

Therefore, the present invention particularly includes proposing a new type of schema that allows for describing a coding format in a comprehensive manner.

The schema according to the invention defines one or various types of data that may have one or various facets. The schema includes a plurality of elements describing the name, data type, nesting, order, and number of predefined or random occurrences, the occurrence of which element being required or optional. And at least one of the following unique features.

Define a data type corresponding to binary segments of infinite length and having at least one facet for the data import mode and optionally a facet for the stop flag of the binary segment.

-Define one or more types of data corresponding to binary words of a predefined length or lengths, having at least one facet of said length and optionally facet of padding bits contained in said binary words.

Define one or more variables configured by the data access path and include one or more conditional branches to describe various structures or possible contents as a function of the variable or values of the variables.

The method according to the invention for syntactically analyzing a bit stream comprising data having a structure and contents according to a particular format, to generate a tree representation of said bit stream,

A) reading a schema, wherein the schema is used to comprehensively describe the format,

 a) defines one or more types of data that may include one or more facets, in particular,

When the format uses binary words of predefined length or lengths, define one or more types of data corresponding to the binary words of predefined length or lengths and having at least one facet with respect to the length, When the binary words of a predefined length or lengths may comprise one or more padding bits, define the data type having facets for the padding bits,

When the format uses indefinite length binary segments having content intended to be imported into the representation using a particular import mode, at least one facet corresponding to the binary segments and corresponding to the import mode. Define a data type having the data type, and when the binary segments are defined by a stop flag, define the data type having one facet for the stop flag,

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 b) includes a plurality of elements describing the name, data type, overlap, order, and number of predefined or random occurrences, the occurrence of the element being required or optional;

c) when the format defines that data located at the beginning of the bit stream gives information about the rest of the content or structure of the bit stream,

 Define one or various variables in the tree representation represented by the access path to the data located at the front,

 The schema reading step comprising one or more conditional branches to describe various possible structures or contents as a function of the variable or the value of the variables,

B) retrieving data in the bit stream corresponding to elements included in the schema;

C) generating an instance of the schema comprising the data found in the bit stream and constituting the tree-like representation.

Thus, the present invention involves creating a tool that allows for a comprehensive description of the format in the schema. The present invention then includes the use of such a schema to parse the bit stream's syntax according to the format to generate a document that represents the stream and is an instance of the schema. The schema specifies the various types of data that may be included in the bit stream, depending on the format, as well as how to include these data in the final document. The rules and data types specified in the schema in the final document depend on the format considered.

For example, when the format considered is the JPEG2000 format (ISO / IEC FCD standard 15444-1), the schema is:

Define various data types corresponding to binary words of predefined lengths that may include padding bits and having one or more facets on the padding bits and a facet on the length,

Data with infinite length binary segments defined by a stop flag with contents intended to be imported into the representation through the use of a particular import mode, with facets on the stop flag and facets on the import mode Define the type,

Define one or more variables constructed by an access path in the tree representation for data located at the beginning of the bit stream and providing information about the contents or structure of the remainder of the bit stream,

Include one or more conditional branches to describe the various structures or contents possible as a function of the value of the variables.

A method according to the invention for generating a bit stream in a particular format from a document that is a tree representation of the bit stream and that contains data, in particular data imported by use of a particular import mode,

A) reading the document,

B) reading the schema in parallel for comprehensively describing the format,

 a) define one or more types of data that may have one or more facets, in particular,

 A data type corresponding to infinite length binary segments having at least one facet relating to the import mode,

 When the format uses binary words of predefined length or lengths, define one or more types of data corresponding to the binary words of predefined length or lengths having at least one facet with respect to the length, When the binary words include one or more padding bits, define a facet for the padding bits,

b) parallel reading the schema, comprising a plurality of elements describing the name, data type, overlap, order, and number of predefined or random occurrences, the occurrence of the elements being essential or optional;

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C) coding said data as a function of said defined type;

D) constructing a bit stream from the coded data.

Accordingly, the present invention also encompasses the use of a schema of the type described above to generate a bit stream from a document that represents a bit stream and is an instance of the schema. The document and schema are read in parallel to determine the data types contained in the document, coding them as the format defines and constructing the bit stream with the coded data.

These and other aspects of the invention will be apparent from and elucidated by way of non-limiting examples, with reference to the embodiment (s) described hereinafter.

1 is a block diagram summarizing the basic mode of operation of a parsing method according to the present invention;

2 is a block diagram summarizing the basic mode of operation of a method of generating a bit stream in accordance with the present invention.

3 is an illustration of a transmission system according to the present invention.

1 is a block diagram illustrating a basic mode of operation of a syntax parsing method according to the present invention. Block B1 represents a bit stream according to a predefined format. Block B2 represents a schema that comprehensively describes the predefined format. Block B3 is a syntactic analyzer that allows the parsing of the bit stream B1 to generate a document B4 that is a tree representation of the bit stream B1 and is an instance of the schema B2. Indicates.

Schema B2 describes the syntax of the bit stream. This specifically specifies the types of data that can occur in the bit stream and how they will be included in the document. The tree representation B4 is generated depending on the analysis of the bit stream B1.

2 is a block diagram for explaining the operation principle of the bit stream generation method according to the present invention. Block B'2 represents a schema that describes the coding format in a generic manner. Block B'4 represents a document that is an instance of schema B'2. Block B'3 represents a bit stream generator that allows reading of document B'4 and schema B'2 in parallel to generate bit stream B'1. Advantageously, the schemas B2 and B'2 used for the same coding format are the same.

Document B'4 is read into schema B'2 to determine the type of data contained in document B'4. For the value read from document B'4, the corresponding type of data found in schema B'2 determines the coding mode to be used to code the value.

Providing complete details of the structure of the comming format in the schema is generally not certainly necessary. The degree of detail depends on the application under consideration. For use as described in French Patent Application No. 0101530 (the method of generating a file, eg a JPEG2000 file, has inherent features adapted to the recipient's profile) already cited at the beginning of this application, JPEG2000 markers Specific segments of) will be given in detail for each parameter to allow the parameters to be recovered and they can be modified. The other segments of the markers are treated as blocks, since it is not necessary to have access to the parameters they contain.

Documents B4 and B'4 are advantageously XML documents, and schemas B2 and B'2 are written in a new language derived from the XML schema language. XML is the Consortium W3C's recommendation (eXtensible Markup Language 1.0 dated 10/06/2000) and XML Schema is the same W3C Consortium recommended project dated 10/06/2000. The XML Recommendation and XML Schema Recommendation Project are available on the Internet at http://www.w3.org/ . However, this is not limitative and the principles of the invention described in detail in the remainder of the description are proposed, for example, by BRICS and AT & T of the University of Aarhus, Denmark, and on the Internet site http: // www. It can be utilized by utilizing different types of languages, languages of type Document Structure Description (DSD), available on brics.dk/DSD/ .

From a physical point of view, an XML document can in particular be analyzed and contain text, ie a sequence of characters belonging to a predefined set of characters, and include entities representing data of a tag or text.

From a logic point of view, an XML document includes one or more elements whose restrictions are marked by a start flag and a stop flag. Elements may be included in other elements (that make up the nesting). Each element is identified by the name indicated in its start flag and stop flag. An element may have a value. The value of an element is placed between its start flag and stop flag.

In the example described below, the data is selected to be placed directly in the elements of the XML document to simplify execution (ie, the data contained in the XML document constitutes the values of the XML elements).

XML Schema is a schema language that allows specifying content and XML document structure, and in particular, XML Schema is intended to describe elements and the number, name, data type, nesting, order, and number of occurrences for each element. Allow. The order and number of occurrences may or may not be predefined. Generation of elements may be necessary or optional.

The schema defines the class of XML documents. An instance of an XML schema is a valid XML document for that schema.

In the following description, and to provide a specific example of implementing the present invention, bit streams in the JPEG2000 format will be considered. This is no longer limited and it is clear that the present invention can be applied to other formats. For certain formats, it may be necessary to add other types of data to those described herein.

In Appendix A (Schema), an example of a schema describing the JPEG2000 coding format is given. This schema is generic and utilizes simple types of data as defined in Appendix B and simple types of data derived from these generic types as defined in Appendix C. Appendix D provides an example of an XML document that is an instance of the schema given in Appendix A and represents a JPEG2000 bit stream. In Appendixes A, B and C and the following description, the letters << xsd >> identify the tools defined in the XML schema. And the letters << bsd >> identify the tools added by the present invention.

According to the present invention, schema B2 (considered to be the same as schema B'2 in the following description) defines all data types that can be included in the stream according to the JPEG2000 format. Certain types of data already exist in the XML Schema language and can be used directly. Others will be corrected. Others must be added.

Bit streams according to the JPEG2000 format include in particular the following types of data.

1) Infinite length binary segments in which its contents can be imported in an XML document through the use of a first or second import mode described below.

2) Binary words of different lengths that may include non-significant padding bits.

3) Markers whose values are defined in hexadecimal code in the JPEG2000 standard and imported in hexadecimal code in an XML document. This import into hexadecimal code constitutes a third import mode.

 The first import mode includes converting binary data into characters that belong to a predefined set of characters used by XML. For this purpose, the coding method is advantageously used under the name << base 64 >> and described in paragraph 6.8 of document RFC 2045 published by the IETF. The method includes dividing binary data, converting them into groups of 6 bits, and associating characters of a predefined set of characters with each group of 6 bits. This first import mode results in an expansion of data by 33%.

In the second import mode, instead of converting the binary data into characters and inserting them directly into the XML document, pointers to regions of the binary file containing the binary data are introduced into the XML document. The XML document then depends on the binary file.

In the XML Schema language, the data type is

A set of values called a value space,

A set of lexical expressions called lexical space,

Is defined as a triplet containing a set of facets corresponding to constraints imposed in the value space.

In order to carry out the invention, the coding of the data written to the bit stream will be clear and implicit. Certain types of data that previously existed in the XML schema and are explicit and implicit are used directly, which, for example, represent an integer between -32768 and +32767 and can therefore be implicitly coded into two bytes, < This is the case with the <xsd: unsignedShort >> data types. This is also the case with << xsd: unsignedInt >> and << xsd: unsignedByte >>.

According to the invention, the data type << xsd: binary >> is also used by modifying it.

1) A facet about a stop flag named << bsd: stopFlagExclusive >> is added. This facet will be used to mark the end of an infinite length binary segment. For example, JPEG2000 packets, which are infinite length binary segments, may be marked by a marker start of packet (SOP) or marker start of tile (SOT). , By the start of a tile) or by the marker End of Code stream (EOC), so for a JPEG2000 packet this facet has three values: FF51 (SOP), FF90 (SOT) or FFD9 ( EOC).

2) A new possible value is added to the << encoding >> facet already existing in the XML Schema language with << base 64 >> for import and << hex >> for hexadecimal code after base 64 conversion. . The new added value is called << externalData >>. This is used to indicate that data is to be imported into the XML document by use of the second import mode mentioned above (introduced in an XML document of a pointer pointing to the bit stream area containing the relevant data).

This modified type of data is named << binaryNoLength >> and is defined in Appendix C in the following manner.

This modified type of data, which is a generic type, is then used to derive other types of specific data that can be found in the XML bit stream. For example, as indicated in Appendix B, the type << PacketDataTYpe >>, corresponding to JPEG2000 packets, is derived from the generic type << binaryNoLength >>. In this example, it is noted that the data contained in these packets is imported into the XML document by the use of a second import mode (pointer to the area of the bit stream containing the data). It is also known that the JPEG2000 packet is defined by a marker having one of the following three values FF51, FFD9 or FF90.

While referring to Appendix A, it is found that other elements have an element named << Data >> in an element derived from << binaryNoLength >>, for example a compound COC type. This element << Data >> has a facet << encoding >> whose value is << base 64 >>, which means that the corresponding data is imported from the bit stream in the XML document using the base 64 transform. .

The invention also includes the addition of a new type of data intended to be used for binary words of predefined length. This new type of data is named << bsd: bitsArray >>, which contains three facets, one facet named << bitsLength >>, which is related to the length of a binary word, and << prePadding >>. One facet named relates to the number of padding bits located before the higher bits or bits, and one facet named << postPadding >> relates to the number of padding bits located after the upper bits or bits. This new type of data is defined in Appendix C in the following manner.

As indicated in Appendix B, this new type of data, which is then a generic type of data, is used to derive certain types of data that can be found in the JPEG2000 stream. For example, a data type named << 11b >>, derived from the generic type << bitsArray >> of data, corresponds to an 11-bit binary word that does not contain padding bits.

And, a data type named << 5b3p >>, also derived from the generic type << bitsArray >> of the data, corresponds to a binary word of 5 bits that includes two higher bits followed by three padding bits.

Referring to Appendix A, data type << 11b >> is used, for example for an element named << mantissa >>,

<xsd: element name = "mantissa >> type =" jp2: 11b "/>,

The data type << 5b3p >> is used, for example for an element named << exponent >>,

It is found to be <xsd: element name = "exponent >> type =" jp2: 5b3p "/>.

From a structural point of view, the present invention utilizes the following tools that already exist in the XML schema.

Simple and complex types of data << xsd: simple Type >> and << xsd: complex Type >>,

Elements << xsd: element >>,

Group models << xsd: group >>,

Connectors << xsd: sequence >>, << xsd: all >> and possibly << xsd: choice >>.

Syntactic analyzer B3 reads bit stream B1 into schema B2 to generate a tree-like representation B4 of bit stream B1. This tree representation B4 is an instance of schema B2. This occurs recursively by interpreting the connectors found in the schema.

In particular, the connector << xsd: sequence >> is interpreted by the parser in the following manner. When the parser finds the connector << xsd: sequence >>, it reads the elements in the bit stream in the same order as the schema. For example, the connector << xsd: sequence >> is used in elements of type << Codestream Type >> as defined in Appendix A.

According to this definition, an element << Codestream >> may include an element << MainHeader >> followed by << Title >> and followed by << EOC >>.

The connector << xsd: all >> is interpreted by the parser in the following way. When the syntactic analyzer finds the connector << xsd: all >>, it starts by trying to read the first declared element in the connector << xsd: all >>, and if that fails, attempts to read the second element, etc. do. When it finds an element to be searched, it advances to the next element in the connector << xsd: all >>. Only when all elements of the connector << xsd: all >> have been reviewed will the next connector go on.

An element found in the bit stream is searched when the schema defines a fixed value for this element or for one of the subelements it contains, and when this value does not correspond to that found in the bit stream. Does not correspond to the element being For example, when the parser tries to perform an element << SIZ >>, the element read from the bit stream does not begin with << FF51 >>, which is the value assigned to the marker << SIZ >> in the JPEG2000 standard. It is not a searched element.

The connector << xsd: all >> is used, for example, in elements of type << MainHeader Type >> as defined in Appendix A.

According to this definition, the element << MainHeader >> is followed by the element << SIZ >>, followed by a group which may contain one or more of the following elements, taken in a random order, or which may not contain anything. It must contain the following elements << SOC >>: << COD >>, << QCD >>, << COC >>, << QCC >>, << RGN >>, << POC >>, << PPM >>, << TLM >>, << PLM >>, << CRG >>.

No example is given at all in Appendix A, but the connector << xsd: choice >> can also be used. When the parser finds the connector << xsd: choice >>, it begins trying to read from the bit stream the first element declared in the connector << xsd: choice >>. When the parser finds an element to be searched, it goes on to the next connector in the schema. When the element read is not the element being searched for, the parser advances to the next element in the same connector << xsd: choice >>.

The present invention also introduces the use of variables in schemas. The concept of variables is used in the XSLT (XML Extensible StyleSheet Language Transformation) language. XSLT is a language specified by the W3C Association, which allows defining transformations that can be applied to XML documents. In concrete terms, a variable is a character string concatenated into a value. It can appear at a specific location within the document and can be used elsewhere. According to the syntax defined in the XSLT, the value of the identified variable by the character stream is accessed by placing a $ symbol before the character string (in other words, $ ZZZ is the value of the variable identified by the character string ZZZ). The value of the variable is displayed in the definition of the variable. The present invention allows defining the value of a variable in the form of a path in an XML tree by using a syntax defined in the Xpath language (XML path language). Xpath is also a language specified by the W3C Association. Specifications of XLST and Xpath are available on the Internet at http://www.w3.org .

The use of variables, for example, allows defining many elements by parameters instead of by constant values. When the value of a parameter is given at the beginning of the bit stream and informs about the rest of the structure or contents of the bit stream, the value of the variable is defined by the use of Xpath syntax.

For example, the number of elements << comp-siz >> included in the marker segment SIZ in the JPEG2000 format is defined by a parameter << Csiz >> located in front of the marker segment SIZ. In Appendix A, the element << Csiz >> is defined as a variable. The value is defined by the path in the tree-like representation being constructed, where the indication << SIZ / Csiz >> indicates that << Csiz >> is the son element of the element << SIZ >>. Then, during the definition of the complex type << SIZ >>, this variable << Csiz >> is called to determine the number of occurrences of the element << comp-siz >>.

The invention also includes the addition of a new group model << bsd: conditionalChoice >> and two new connectors << xsl: if >> and << xsl: choose >>. This introduces conditional branches in the schemas and thus allows for expressing conditional choices that may exist in the format to be described. It will be noted that the connectors << xsl: if >> and << xsl: choose >> are defined in the XLST language. In accordance with the specifications of the XSLT language, the connectors << xsl: if >> and << xsl: choose >> use the attributes << test >> which allow to define the selection of a function of the result of the test. The connector << xsl: if >> allows defining a selection as a function of the value of a Boolean variable. The connector << xsl: choose >> allows to define the selection from a plurality of alternatives.

As an example, the JPEG2000 format provides that the presence or data type of certain elements depends on the value of the parameter given earlier in the bit stream.

This is especially the case for the element << SPcod >> contained in the << COD >> element. The element << SPcod >> contains the element << PredinctSize >> only if the variable << PredinctsUsed >> has a value of 1. This constraint is expressed in the schema in which the connector << xsl: if >> is used.                 

In element << QCD >>, the position in the tree representation that the type of elements to follow (Spqcd_1 >>, Spqcd_2 or Spqcd_3) is currently processed is given by the parameter << given by the path << QCD / Sqcd / QuantStyle >> An example of a group << bsd: conditionalChoice >> using connectors << xsl: choose >> to indicate that it depends on the value of quantStyle >> is found.

When the parser reads the bit stream, it generates an XML tree progressively. In the schema, for example in the property << test >> of the connector << if >>, when finding the variable, the value of this variable is obtained by using the indicated path.

It will be noted that the XML language allows for defining its own extensions. Thus, the first embodiment of the present invention includes the addition of new tools proposed by the present invention as extensions to the existing XML Schema language. Another embodiment of the present invention involves the overall redefinition of a new language that takes the tools of an XML schema and adds them to the new tools proposed by the present invention.

In figure 3 an example of a transmission system according to the invention is shown. The transmission system shown in FIG. 3 includes a server SV and a plurality of clients CT. The server SV and the clients CT are connected to the Internet WWW. The server SV includes a memory means MEM and a processing means PROC. The memory means is in particular the syntax according to the invention to obtain a first document B4 representing the schema B2, the first bit stream B1 and the first bit stream B1 and which is an instance of the schema B2. Computer program PG1 for performing the analysis method. The memory means MEM also advantageously comprises a computer program PG2 which performs the method of generating the second bit stream B'1 from the document B'4 indicating the same and from the schema B2.

By way of example, document B'4 is obtained by using a transformation to document B4, which transformation depends on the profile of the client that previously requested delivery of the bit stream.

Claims (12)

A method of parsing a bit stream comprising data having structure and contents according to a predefined format, the syntax being intended to generate a document comprising a tree-like representation of the stream. In the analysis method: A) reading a schema to describe the predefined format, The schema comprises a plurality of elements describing the name, data type, overlap, order, and number of predefined and random occurrences, the occurrence of the element being required or optional, The schema defines one or more variables configured by each data access path (s) and defines one or more conditional branches that describe various structures or possible contents as a function of the variable or values of the variables. Comprising, the schema reading step; B) obtaining values for the one or more variables defined in the schema from the bit stream by using the respective data access path; C) among the various structures and possible contents in the schema by interpreting variables in the schema as a function of the obtained values and evaluating conditions of the conditional branches in the schema as a function of the obtained value. Selecting structures and contents; D) retrieving the data in the bit stream corresponding to elements included in the schema; And E) generating a document comprising data found in said bit stream and constituting said tree-shaped representation defined by said schema. A recording medium having recorded thereon a computer program comprising instructions for causing a processor of a computer to execute the parsing method as claimed in claim 1. A method of generating a bit stream in accordance with a predefined format from a document that is a tree-like representation of the bit stream and includes data: A) reading the document; B) reading the schema in parallel to describe the format, The schema defines one or more data types that may have one or more facets and comprises a plurality of elements describing the name, data type, nesting, order, and number of predefined and random occurrences; The occurrence of an element is mandatory or optional. The schema defines one or more variables configured by each data access path (s) and includes one or more conditional branches that describe various structures or possible contents as a function of the variable or values of the variables, Determining the data type included in the schema parallel read step; C) coding the data as a function of a type defined in the schema; And D) constructing a bit stream from the coded data. A recording medium having recorded thereon a computer program comprising instructions for causing a processor of a computer to execute the method of generating a bit stream as claimed in claim 3. delete In the processing unit: As memory means for storing a bit stream, storing a tree representation in a document, and storing a schema describing the format, The schema defines one or more data types that may have one or more facets, and includes a plurality of elements describing the name, data type, nesting, order, and number of predefined and random occurrences, Occurrences are essential or optional, The schema defines one or more variables configured by each data access path (s) and includes one or more conditional branches describing various structures or possible contents as a function of the variable or values of the variables, Memory means; Read the schema from the memory, read a bit stream from the memory, and for the one or more variables defined in the schema from the bit stream where the location of the value of the variable is defined by the respective data access path. A structure among the various structures and possible contents by obtaining values, interpreting variables in the schema as a function of the obtained values and evaluating the conditions of the conditional branches in the schema as a function of the obtained values Fields and contents, retrieve data corresponding to elements in the schema in the bit stream, generate an instance that constitutes the tree-like representation defined by the schema, and the tree-like representation in a document. A syntax bit string to store in the memory The processing unit including the analyzer. In the transmission system: Source entity; Destination entity; And Transmitting means for transmitting a bit stream from the source entity to the destination entity, The destination entity comprises a processing unit as claimed in claim 6. The method of claim 1, Wherein the schema further defines a data type corresponding to binary segments of infinite length and having at least one facet associated with a data import mode and a facet associated with a stop flag of the binary segment. The method according to claim 1 or 8, The schema further defines one or more data types corresponding to binary words of a predefined length or lengths and having at least one facet related to the length. The method of claim 8, Wherein the schema further defines a facet associated with padding bits included in the binary words of the predefined length or lengths. In the processing unit: As memory means for storing data in a tree representation in a document, storing bit streams, and storing schemas describing the format, The schema defines one or more data types that may have one or more facets, and includes a plurality of elements describing the name, data type, nesting, order, and number of predefined and random occurrences, Occurrences are essential or optional, The schema defines one or more variables configured by each data access path (s) and includes one or more conditional branches describing various structures or possible contents as a function of the variable or values of the variables, Memory means; And Read the schema from the memory, read the document from the memory, code the data as a function of the defined types, construct a bit stream from the coded data, and store the bit stream in the memory A processing unit comprising a bit stream generator. In the transmission system: Source entity; Destination entity; And Transmitting means for transmitting a bit stream from the source entity to the destination entity, The source entity comprises a processing unit as claimed in claim 11.

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