SPDL General Architecture

This clause describes the general architecture of the Standard Page Description Language. In the following clauses, objects and structures which are specific to this International Standard are named by proper names (indicated by names beginning with capital letters), while generic objects are indicated by common names (indicated by names beginning with small letters).

Document Processing Model

The basic document processing model consists of three processes and two forms of document representation as illustrated in . Document Processing Model

The Creation and Editing Process generates the character text and graphics which comprise the logical content of the document, and the logical document structure. This information is represented as a revisable form document. The Composition and Layout Process formats the character text and graphics contained in the revisable form document for presentation, and incorporates the composition and layout decisions in a final form document. The Presentation Process renders the final form document in visible form. These processes are further described below. This model is of necessity greatly simplified. Actual document processing is usually highly iterative. Revisable form documents are formatted for proofing, and the results of the Composition and Layout Process must be presented to be evaluated. Many applications also include multiple processes. Document editing systems frequently include a Composition and Layout and Presentation Process for document previewing, while some printers may combine a Composition and Layout Processes with the Presentation Processes.

Creation and Editing Process

The Creation and Editing Process is responsible for the creation of the character text and graphics which comprise the logical content of the document and for the logical structure of the document. It may also generate information which specifies how the Composition and Layout Process is to format the document for presentation.

Revisable Form Document

The revisable form document represents the logical content and structure of the document created by the Editing Process. It also includes any information generated by the Editing Process which specifies how the document is to be formatted for presentation.

Composition and Layout Process

The Composition and Layout Process composes character text of the document, formats any graphical elements, and lays out the composed character text and graphics for presentation. All composition, formatting, and positioning decisions are made by the Composition and Layout Process. These decisions include such details as

The formatting specifications which direct the Composition and Layout Process may be part of the revisable form document or they may be separate from the document. ISO/IEC 10179 defines one form for formatting specifications which are not part of the revisable form document.

In addition to the revisable form document and formatting specifications, input to the Composition and Layout Process may include previously formatted elements which are to be incorporated in the final form document.

Final Form Document

The final form document represents the results of the composition, formatting, and positioning decisions made by the Composition and Layout Process. It is not required to represent the logical document structure, the formatting specifications, or the intent of those decisions.

Presentation Process

The Presentation Process presents an document by rendering it in visible form on suitable media. It also performs any finishing operations (e.g. trimming, stapling, or binding) which are part of document presentation.

SPDL Document

SPDL is a final form document format. As such it provides facilities for the efficient representation of the decisions made by the Composition and Layout Process. SPDL does not provide facilities for the representation of logical document structure.

Sources of SPDL Documents

The primary source of SPDL documents is the application of a Composition and Layout Process to a revisable form document. In addition, an SPDL document may also be created by:

SPDL Document Presentation

The SPDL document represents the ideal image specified by the Composition and Layout Process. It is the responsibility of the SPDL Presentation Process to adapt the rendering of the document to the constraints of the presentation device so as to provide the best possible approximation to the description specified by the Composition and Layout Process.

An SPDL document may be presented many times, at different times and/or places. For this reason document presentation must accommodate parameters which may be specific to a particular instance of presentation. These parameters are specified by Document Production Instructions.

Document Production Instructions may be conveyed to the Presentation Process as part of the SPDL document or made available via a separate mechanism. The method by which Document Production Instructions which are not a part of the document are made available to the Presentation Process is outside the scope of this International Standard.

Uses of SPDL Documents

The primary use of SPDL documents is input to an SPDL Presentation Process. In addition, an SPDL document may be used to represent a formatted portion of document content. Such previously formatted document content may be used as input to a Composition and Layout Process for inclusion in another document.

SPDL Document Architecture

An SPDL document has structure and content. The structure organizes the content into separable parts and identifies the resource requirements for each part. The structure is self contained and can be processed without processing the content.

The content is in the form of a page description language which specifies how the page images are to be generated. The processing of the content is dependent on the processing of the structure: the processing of the structure establishes the context in which the content can be processed.

The Presentation Process may also have available to it various sources of additional data, such as fonts or stored portions of SPDL documents, which may be referenced by an SPDL document. The sum of all such data is called the environment of the Presentation Process.

Document Structure

The document structure is the result of the division and repeated subdivision of a document into increasingly smaller parts. The resulting parts are called structure elements. An example of the document structure is shown in . Example of SPDL Document Structure

The document structure is hierarchical. The highest level structure element is a DOCUMENT. A DOCUMENT may contain subordinate PAGESET and/or PAGE structure elements.

A PAGESET may in turn contain subordinate PAGESET and/or PAGE structure elements. Each PAGE contains the description of that portion of the document which is to be presented on a single instance of the presentation medium.

A PAGE may contain subordinate PICTURE and/or TOKENSEQUENCE structure elements. A PICTURE may contain subordinate PICTURE and/or TOKENSEQUENCE structure elements. A TOKENSEQUENCE is a structure element which contains document content.

DOCUMENT and PAGE structure elements are semantically distinct but are not syntactically distinguished. A DOCUMENT is simply a PAGESET or a PICTURE which is at the highest level in the structure hierarchy. Similarly, a PAGE is simply a PICTURE which is at the highest level in the PICTURE hierarchy.

In addition to representing the division of an document into smaller parts, the document structure supports:

Processes which process SPDL structure for purposes other than document presentation (e.g. a Composition and Layout Process which extracts PICTURE structure elements for inclusion in other documents, or an Imposition Processes which produces a new document by combining multiple page images on a single sheet) are outside the scope of this International Standard.

Document Content

The content of a document is the data contained in TOKENSEQUENCE structure elements. Document content within each TOKENSEQUENCE consists of a sequence of tokens. Document content processing consists of interpreting the sequence of tokens in each TOKENSEQUENCE. The overall process of token interpretation is modeled as a virtual state machine.

External structure elements

An External Structure Element is a structure element which is included in an SPDL document by reference. An SPDL document that includes an External Structure Element by reference must declare it in an EXTERNAL DECLARATION structure element.

Resources

A resource is an information object which is available in the environment of the Presentation Process. Resources may be defined as specified in this International Standard or may be made available in the environment of the Presentation Process by means of a processes which is outside of the scope of this International Standard. A resource may be used, by reference, within the document content of an SPDL document. An SPDL document that references a resource must declare it in a RESOURCE DECLARATION structure element.

Document Presentation

Since the SPDL document consists of document structure and document content, and since these categories of data are separable, the Presentation Process can be modeled as containing subsidiary processes which process structure and content separately. In this International Standard, these processes are referred to as the Structure Processor and the Content Processor respectively. The Presentation Process also contains Marking and Finishing Process which renders the page images on the medium and performs any document finishing processes. See ). SPDL Presentation Process While structure processing and content processing are logically separable processes, separate processes need not exist within an implementation of the Presentation Process. The only requirement is that presentation of SPDL documents occurs with the results specified in this International Standard.

Document structure processing consists of analyzing the structure elements of the SPDL document, their types, their hierarchical relationships, and the presentation order. For presentation, structure processing also:

Document content processing consists of interpreting each content element as a sequence of tokens in the Content Representation and Interchange Format and processing those tokens as specified in through .

Document presentation includes all of the artifacts of the Presentation Process, including the generation of error messages and warnings.

Representation and Interchange Format

SPDL documents are interchanged in the Representation and Interchange Format defined in and . The Representation and Interchange Format has two forms, a binary form and a clear text form, and two parts, a Structure Representation and Interchange Format and a Content Representation and Interchange Format. The binary form of the Content Representation and Interchange Format is used with the binary form of Structure Representation and Interchange Format. The clear text form of the Content Representation and Interchange Format is used with the clear text form of the Structure Representation and Interchange Format.

The binary form of the Structure Representation and Interchange Format uses Abstract Syntax Notation 1 (ASN.1) as defined in ISO/IEC 8824 encoded using the Basic Encoding Rules specified by ISO/IEC 8825. The clear text form of the Structure Representation and Interchange Format uses Standard Generalized Markup Language (SGML) as defined in ISO 8879 encoded using ISO/IEC 646 IRV.

The Content Representation and Interchange Format uses specialized encodings optimized for compactness and efficiency for each of the binary and the clear text forms.

Relationship to Print Services

A Print Service which has the capability of printing SPDL documents has an SPDL Presentation Process as part of the Print Service. This clause discusses the relationship of such a Print Service to the embedded SPDL Presentation Process.

Document Production Instructions

When an SPDL document is printed by a Print Service, the print operation parameters may include parameters which affect document imaging and presentation. Such parameters specify Document Production Instructions which are called Supplementary DPI. The Print Service implementation is responsible for making the SPDL document and Supplementary DPI available to the SPDL Presentation Process.

The SPDL Presentation Process resolves interactions between Document Production Instructions which are provided as Supplementary DPI associated with a particular instance of presentation and any Document Production Instructions contained in the SPDL document. This relationship is illustrated in . Relationship of SPDL Documents to a DPA Print Service

Relationship to ISO/IEC 10175

ISO/IEC 10175 defines a standard Document Printing Application which provides a standard (abstract) Print Service. Document printing is accomplished by the invocation of a Print Operation accompanied by a document and a set of Print Operation Parameters.

The Print Operation Parameters defined by ISO/IEC 10175 consist of Print Job Management Instructions and Document Production Instructions.

Print Job Management Instructions do not affect the presentation of SPDL documents. Some, but not all, of the Document Production Instructions defined by ISO/IEC 10175 are applicable to an SPDL Presentation Process.

The semantics of ISO/IEC 10175 Print Job Management Instructions and the general semantics of those Document Production Instructions which may occur as ISO/IEC 10175 Print Operation Parameters are defined by ISO/IEC 10175. The specific semantics of those Document Production Instructions which may occur as ISO/IEC 10175 Print Operation Parameters and which are applicable to the presentation of SPDL documents, when used in the presentation of SPDL documents, are defined by this International Standard.