SLIC
    Standard Language for Implementation Conventions
                    (worktitle)



 
                  Alex Th. de Jong
             dejong@snad.ncsl.nist.gov

                  September 1994


                  Master's Thesis

        Tele-Informatics and Open System Group
        University of Twente, The Netherlands


 Distributed Applications Research and Technologies Group
        Systems and Network Architecture division
   National Institute of Standards and Technology, U.S.A.





Electronic Data Interchange within NIST

NIST has developed an Electronic Data Interchange (EDI) tool called Transaction
Set Development System(TSDS), which is able to define and process X12 or EDIFACT 
interchanges. To define a Transaction Set (or message in EDIFACT) the graphical
interface tools of the Definition Environment (DE) can be used. This
environment enables a user to fully specify a Transaction Set and verify
its compliance with the X12 or EDIFACT standards. 
To process a Transaction Set, the Operational Environment (OE) is available.
The OE consists of specific generated code for Transaction Sets defined
within the DE and a generic graphical interface to edit element values.
Interchanges can be constructed, sent and received using this tool.


General problems of EDI Standards

EDI tools available in the marketplace, in general, have functionality 
similar to the functionality described above. The main differences between
the NIST TSDS prototype and the commercially available EDI software are the 
parser based  decoding and database mapping of EDI transaction sets together
with a generated Application Programmer Interface (API) (versus conventional
table-driven translation). Both the TSDS and commercial products, need to 
be flexible in order to handle upgrades and changes of the publicly 
available standards.

Another problem is the wide variety of ways inwhich the standards are used. 
Within most EDI implementations, standards are adjusted in such a way that they
meet specific requirements instead of using the exact standard. EDI product
vendors therefore need some kind of mechanism to handle these variations of
the standard.

The TSDS uses an intermediate language that can hold an implementation
convention. This language (called  `Script') is a simple representation
of an EDI transaction set in a machine processible format. The parser
together with the language can be used to save and retrieve an 
implementation convention. Similar mechanisms are used within commercially 
available products to handle the problem. Unfortunately, every product uses 
a proprietary technique to solve the problem, which causes incompatibility 
between the software.


Standard Language for Implementation Conventions

A Standard Language for Implementation Conventions (SLIC) can reduce
a number of problems resulting from the wide variety of changing 
standards. By providing a standardized implementation convention, EDI
vendors only need to provide an interface/parser for this language to
update and/or adjust their products.

The language should be flexible and powerful enough to carry different
implementations of one standard. A comprehensive constraint syntax should
be available to refine an existing standard. The constraints should be 
context sensitive to account for the fact that within different 
implementations, segments or elements can be used differently (e.g. a subset
of codes can differ in each implementation instance of an identifier data
element).
 
NIST intends to maintain the output of the language (SLIC) as a defacto 
standard. EDI users will have dial-in (or internet) access to a registry
that holds copies of the implementation conventions. To update an EDI 
product, vendors only need to integrate their code with the publicly 
available parser and then download the implementation convention. The 
registry, maintained by NIST and industry, will contain the latest 
government and industry  implementation conventions.


Project objectives

 o   Design of a syntax for a language that allows the complete description
     of EDI implementation conventions in a machine processible format. This 
     phase contains analysis of existing languages and allows industry to give
     comments.}
 o   Implement a parser for the language that will be used within NIST TSDS.
     This tool is able to generate code for a parser based decoder according
     to the language profiles. The parser which will be put in public domain,
     should be able to function in different software environments, which will 
     enable EDI vendors to use it for their own purposes.
 o   Integrate parser with the NIST TSDS.


Schedule

September to November 1994 : Definition of language (draft version for review)
December 1994              : Final Language definition
January to March 1995      : Completion of parser
March 1995                 : Completion of Master's Thesis 
April to September 1995    : Integration of parser in the TSDS *

* The integration of the parser and defined language within
  the NIST TSDS will be part of the overall project but not of 
  the Master's Thesis. It is placed here to clarify the use of SLIC.


The language definition will take some time in order to get comments from 
industry, but the first draft should be available for review in November.


Abbreviations

API  	Application Programmer's Interface
DE	Development Environment (of TSDS)
EDI    	Electronic Data Interchange
NIST 	National Institute of Standards and Technology
OE  	Operational Environment (of TSDS)
SLIC  	Standard Language for Implementation Conventions
TSDS    Transaction Set Development System