Commentaries

297

O D A - The ISO Standard for Electronic Document Interchange *

Richard C A R R

Standards Division, The National Computing Centre Ltd., Ox- ford Road, Manchester, M1 7ED, UK

The Office Document Architecture Standard (ODA) is expected to become a full ISO International Standard (IS 8613) at the end of 1987. It is currently (June 1987) at the 2nd Draft International Standard (DIS) stage and as such can be considered technically stable and suitable for implementation.

Collaborative projects have been underway for some time and have demonstrated the usefulness of the standard. Manu- facturers are already developing ODA editors and translators for both future and existing systems to comply with emerging application profiles, such as those defined in TOP (Technical & Office Protocol) and GOSIP (the UK Government Open System Interconnection Protocol) that will be used in user procurement specifications.

This article presents an overview of ODA and shows how the architectural model can be used to facilitate document interchange between open systems.

Keywords: Office Document Architecture, Electronic Docu- ment Interchange, Application Profiles, Document Structures, ISO TC97 SC18.

The author is a Senior Consultant in the Standards and Test Development Division at the National Computing Centre. He is currently designing pro- totype implementations and confor- mance test tools for the ISO ODA standard and is co-author of the forth- coming 'Formal Specification of ODA'. He is a member of the TOP DA subcommittee and is currently writing an ODA application profile for the UK Government's Central Communications and Telecommunica-

tions Agency. He holds a B.Sc (hons) in Mathematics and an M.Sc. in Computer Science. Before joining NCC he lectured at Bolton Institute of Technology and worked on a variety of communications systems for Hitachi/AWA in Australia and British Telecom in the U.K.

* [Editor's Note: The discussion on ODA will be continued in the next issue of this Journal with the paper FODA - The Formal Specification of ODA Document Structures and Its Use as a Basis for Conformance Testing by W. Appelt.

North-Holland Computer Standards & Interfaces 7 (1988) 297-301

1. What is ODA?

O D A is an ISO Standard for in terchanging 'w ha t you see is what you get' integrated text and

graphics documents between dissimilar systems in an Open Systems In te rconnec t ion (OSI) environ- ment . The O D A Standard provides for the inter- change by prescribing an independen t model of the content , logical and layout sub-structures found in typical office documents . Al though ini- tially designed for office systems, O D A is now viewed as being appropria te for the interchange of complex workstat ion documents such as those found in the aerospace industries.

O D A ' s abstract model caters for documents such as memos, newsletters, technical papers and

reports, manuals , presentat ions etc. where the con- tent might include mixtures of character text, facsimile and drawings. Important ly , O D A pro- vides for processable document interchange where the paragraphs and page layout in format ion can be transferred between previously incompat ib le systems, edited and reformatted by these systems and make round trips between systems without losing in format ion the users did not in ten t ional ly delete.

2. Why We Need O D A

Without a common model for in terchanging documents the solut ion usually adopted for elec- t ronic transfer is the use of convertors between each pair of different systems. This involves writ- ing software to convert system A's documents into system B's and if two way working is needed, writ ing a B to A conversion. Al though this ap- proach is adequate for a small n u m b e r of systems where it might offer a low level of conversion degradat ion the method presents a serious disad- vantage if more systems are added to the set in use. In the case of n different document systems,

0920-5489/88/$3.50 © 1988, Elsevier Science Publishers B.V. (North-Holland)

298 R. Carr / ODA

each will require n-1 conversion programs for transfer to and from the n-1 remaining systems, i.e., n times n-1 programs in all. The cost of this approach grows exponentially with the number of interchange systems. Fifty-six pieces of software would be needed for eight systems, three-hundred and eighty for twenty sytems! A standard inter- mediate form keeps the cost to the software in- dustry linear at two convertors per system. How- ever, it is important that whatever intermediate form is used, it should not simply be a common subset of the n document structures but be power- ful enough to avoid the information loss that is present with any nontrivial conversion. ODA with its clear separation of document and content ar- chitectures and with its powerful set of attributes satisfies such a requirement.

3. Elements of the ODA Model

3.1. Document Profile

The ODA model describes a document in terms of a document profile and a document body. The profile is used for document management, specify- ing those characteristics of the document that apply to it as a whole such as filing and retrieval details, security aspects and external references. It also details the type of structures and content present in the document body and for this reason may be interchanged on its own. This allows a recipient system to interpret the information in the profile and subsequently determine whether it wants to receive the document body.

The ODA Standard allows the profile to iden- tify which particular document application profile (DAP) an originator has used. A DAP defines a subset of the structures and features available in ODA and is used to tailor ODA to a particular user's or organisation's needs. Currently DAPs are being defined by such organisations as CCITT, TOP, SPAG, the U K and European Governments, BT, NBS etc. It is envisaged that these APs will be functionally equivalent within classes; two have already been fairly well defined by the groups. These are an application profile for existing wordprocessors and one for the integrated text and graphics documents found on desktop pub- lishing systems. All application profiles will be registered, so any receiving system will know from

the identity of the application profile what type of document to expect. It is thought that most imple- mentations of ODA will configure the interchange systems to handle one or more particular appli- cation profile.

3.2. Document Body

An ODA document body can contain up to three parts: a specific structure, a generic structure and a document style. A document 's specific structure represents a particular document such as a technical journal; the logical elements being the contents fist, individual papers with their titles, abstracts and sections etc. The layout structure of the journal could be seen as the page-sets for each contribution and the areas on the pages used for headings, paragraphs and figures. The content of the specific structure is the character text in the paragraphs and the objects in the figures. The generic structure of a document provides informa- tion that describes a class of documents which, in the case of a journal, might reflect all the general properties of the type of document such as the requirement for each author's name and organisa- tion to appear on the first page of each contribu- tion.

3.3. Document Style

A Document Style refers to the collections of attributes that are used to direct the layout and control presentation of the document 's content. There are two types: layout style and presentation style. An example of a layout style requirement might be the directive to keep a figure and its caption on the same page. A presentation style might specify that the footnotes in a paper are to use an 8pt italic font and that the section titles are to be underlined. By extracting the common style elements it is possible for ODA to save on the transmission costs of interchanging a document since it would not be necessary to send the same information for text which had the same layout or presentation characteristics.

3.4. Specific Structure

As mentioned earlier, ODA views the content in a document 's specific structure in two ways. The specific logical structure associates the con-

R. Carr / ODA 299

tent of a given document with the document ' s logical elements. These might be sections, foot- notes, paragraphs, figures or any other object a system may use to logically part i t ion a document ' s content. O D A also provides the specific layout structure of a document to associate the same content with elements related to the presentat ion media such as pages and columns. Depending on the applications and whether or not further edit- ing of the document is required, a system can transfer either or bo th of the structures. If the specific logical structure is transferred alone then, al though the content can be subsequently altered, its layout will be determined by the recipient 's system. Transferr ing just the specific layout struc- ture will ensure that the layout is "as intended by the originator" but the content will be in image form only and as with facsimile image this inhibits further logical processing.

3.5. Generic Structure

O D A uses a generic structure to describe a class of documents . As previously ment ioned a document class is a set of documents that exhibit c o m m o n characteristics such as pages with the same headers or s tandard paragraphs with con- sistent presentat ion features. These may be such elements as the layout of a c om pa ny memo or particular clauses in a legal contract. I f an organi- sation wants a logo to appear on each page of an interchanged document then there is no need to transmit more than one content por t ion con- taining the logo or one layout object describing its posit ion etc. on the page. As well as improving transmission efficiency by factorising such infor- mat ion that would be c o m m o n to all pages of a document , the generic structure can also be used to maintain the internal consistency of documents since it inherently provides an editing guide and page template for the recipient system. This can be used to preserve an organisat ion's own particu- lar format for documents .

4 . A t t r i b u t e s

One of the ways in which the richness of O D A can be seen is by examinat ion of the particular attributes that model the properties of a document and its structures. If one considers all the logical

Table 1

Attribute Sample application for a para- graph

block alignment

indivisibility

layout category

same layout object

separation

synchronisa t ion

new layout object

specifies alignment of paragraphs within the page;

specifies that a logical object is to be contained within a particular layout object, for example, specify- ing that a paragraph is not split across two pages;

specifies a particular layout object for elements in the paragraph so that, for example, the text of bibli- ographical references can be laid out at the end of a report;

specifies that two logical objects, such as a figure and its reference within a paragraph are to be laid out on the s a m e page;

specifies the minimum distance be- tween logical objects such as a fig- ure, its caption and the following paragraph;

specifies paragraph alignment for multi-column working;

specif ies that a logical object is to be laid out in a new object, for example , that a paragraph is to start on a n e w page.

requirements that might be needed when laying out and presenting a document then the attributes offerred by O D A adequately cover the needs of current wordprocessors as well as features en- visaged for the more sophisticated text and graph- ics systems that have recently entered the market as desktop publishing systems. Table 1 describes a few of the layout directive attributes that might be required by a logical object such as a paragraph.

5 . E x a m p l e D o c u m e n t

An example three-page document is shown in Figures 1-3 . This example has been developed by members of a special working group in ISO T C 9 7 / S C 1 8 / W G 3 responsible for concrete exam- ples of ODA. The full specification and inter- change format for this document are contained in Annexes to the Internat ional Standard. The exam- pie contains raster graphics content in the form of

300 R. Carr / ODA

JUNE 1987

TO : Atl our readers

SUBJECT: EXAMPLETO CLARIFY THE DOCUMENT ARCHITECTURE MODEL

SUMMARY-SUMMARY SUMMARY-SUMMARY-SUMMARY SUMMARY-SUMMARY-SUMMARY SUMMARY-SUMMARY-SUMMARY SUMMARY-SUMMARY-SUMMARY SUMMARY-SUMMARY-SUMMARY SUMMARY-SUMMARY-SUMMARY SUMMARY-SUMMARY

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCC

DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD DDDDDDDDDDDDDDDDDDDDDDDD

FORMAL ENDING-FORMAL ENDING-FORMAL ENDING-FORMAL ENDING-FORMAL ENDING-FORMAL ENDING-FORMAL ENDING-FORMAL

Miss Aude HEA Document Architect

Fig. 1. First page of example document Fig. 3. Third page of example document

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAA

BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB BBBBBBBBBBBBBBB

, , 2

P

1,75 X

caption-caption

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

Fig. 2. Second page of example document

a logo on the first page and a signature on the last page. The second page contains some geometric graphics in the form of a figure with axes, curve and text objects. The rest of the document uses the character content architecture coded to ISO 6937. The second page of the document could be considered to contain four logical objects: namely paragraph A A A A A . . . . paragraph BBBBBB . . . . a composite logical object consisting of a graph and its associated caption and paragraph C C C C C . . . .

split across the second and third pages. The sec- ond page could also be viewed as a composite layout object consisting of areas holding para- graph A, paragraph B, the graph, the caption and the first part of paragraph C. The areas within a page that hold the content are termed frames in ODA. Frames can be composite to nest other frames and can overlap with other frames. In Figure 1 there might be frames defined in the layout structure to hold the logo, date, summary etc. On the last page the formal ending might be a c o m m o n piece of content that might appear on all such documents and for this reason could be held centrally by an organisation.

R. Carr / ODA 301

6. Interchange Mechanisms 7. Summary

ODA documents can be interchanged between open systems in a variety of ways. It will be possible to specify an ODA document as a body type using the CCITT X.400 Electronic Mail Standard or as a document type using the ISO FTAM Standard (ISO 8571). It will also be possi- ble to transfer ODA documents on flexible disk using the File Structure and Labelling for In- formation Interchange Standard (ISO 7665). Whichever mechanism is used, Part 5 of the ODA Standard specifies the interchange format (ODIF) which is expressed in the ASN.1 notation (ISO 8825).

An overview of ODA has been presented show- ing the structures and some of the attributes found in its architecture model. ODA can easily describe the average document found on current word- processing systems. ODA application profiles are already being specified by large user groups such as the European Commission and TOP. The NBS (US National Bureau of Standards) ODA Imple- mentor Agreements will be finalised before the end of 1988. As a result a number of implementa- tions of ODA seem likely to appear in demonstra- tions shortly.