Adapting Legacy Computational Software for XMSF 1 © 2003 White & Pullen, GMU03F-SIW-112 Adapting Legacy Computational Software for XMSF Elizabeth L. White

Adapting Legacy Computational Software for XMSF 1

© 2003 White & Pullen, GMU 03F-SIW-112

Adapting Legacy Computational Software for XMSF

Elizabeth L. White and J. Mark Pullen

Department of Computer Science and C3I Center

George Mason University

Fairfax, VA 22030

[email protected]; [email protected]



Overview

• Background

• Web services, XML and SOAP

• From legacy code to web services

• Experiments to date

• Conclusions



Background - Big Picture Web-based technologies applied within an extensible framework will

enable a new generation of modeling & simulation (M&S) applications to emerge, develop and interoperate.

Support for operational tactical systems is a missing but essential requirement for such M&S applications frameworks.

The framework of Extensible Markup Language (XML)-based languages can provide a bridge between forthcoming M&S requirements and open/commercial web standards, while continuing to support existing M&S technologies.

Compatible and complementary technical approaches are now possible for model definition, simulation execution, network-based education, network scalability, and 2D/3D graphics views.

The Web approach for technology, software tools, content production and broad use provides best business cases from an enterprise-wide (i.e. world wide) perspective.



Background - Goals

Enable use of legacy code in XMSF:

• Approach should be easy to apply

• Platform independence

• Inexpensive or freely available tools



Web Services• Definition: a self-contained, self-describing

unit of modularity for publishing and delivering XML-based digital services over the Internet.

• natural extension of the concept of a resource

• accept messages and return replies– all encoding in XML– peer-to-peer or client-server



Specifying Web Services

• Externally visible behavior is described in terms of the syntax, semantics, and sequencing of messages exchanged between the service provider and its client

• Described using an XML Schema vocabulary• Web Service interface description document

specifies a contract between the service provider and its client.



Web Services Model

Service Provider

Service Provider

Service Consumer

Service Consumer

Service RegistryService

Registry

Bind

Publish Query



XML

• Universal meta-language of the Web • Used for data, content, messaging, and

computing to provide point-to-point integration in a platform-neutral way

• Document structure, content and semantics defined by XML schema

• Basis for a new generation of lightweight, XML-based, application-level protocols now emerging



Simple Object Access Protocol (SOAP)

• XML-based, lightweight messaging protocol for exchange of typed information in decentralized, distributed environments

• Enables interoperability among (existing) distributed applications running on disparate, heterogeneous platforms using a modest infrastructure

• Guiding principles are simplicity and extensibility by modularity.

• Does not define a programming model or require a specific network transport.

• Simply consists of a modular packaging mechanism and a set of encoding rules.



SOAP Benefits• Provides a message format, type information and

encoding mechanism• Allows platforms-independent information exchange

information, irrespective object model or programming language

• Packaging mechanism allows for expressing complex communication semantics ranging from RPC-style calls to general message passing (with or without queuing)

• Encoding rules, define a data serialization format for exchanging application or platform-specific datatypes.

• SOAP message (encoded as XML document) is a one-way transmission routed along a message path



From Legacy Code to Web Services

• Approach centers on Java and a publicly available SOAP implementation

• Service consumer sends and receives SOAP messages

• Service provider has a Java front end that processes requests

• Experimental implementations of FORTRAN and C++ services



Java-Based Web services

ServiceConsumer

ServiceProvider

LegacyCode

SOAPMessages



Source-to-Source Transformation

• Option 1: reimplement the functionality in Java– automatically via source-to-source

transformation techniques or by hand– resulting executable can be run on any

architecture that supports Java• even if it does not have a compiler for the legacy

language.

– tried this first



Source-to-Source Transformation Problems

• FORTRAN to Java tools exist– we used f2j – not completely automatable– data type and control flow limitations

• Source code access limited or nonexistent• No good way to test the transformed code

– legacy code provided no test cases

• Potential performance problems– Java is an interpreted language



Java Wrappers for Legacy Code • Option 2: Java Native Interface (JNI) user

creates Java wrappers to use the native code executable directly– C, C++ and FORTRAN

– appears to be most automatable approach

• results in a faster component– but it may not be portable

– so, run the service on a platform that supports it

• legacy code has already been tested and accepted – reduces the amount of testing required for the Service



Java Web Services

• Transformation of Java component into a Web Service is a relatively painless process

• Tools closely track the emerging standards for web-based interaction

• Quite straightforward to use – developers to know only minimal XML and SOAP

• We used Axis– third generation of Apache SOAP.



Cannon Example(Bourg, Physics for Game Developers, O’Reilly, 2001)



Conclusions• Transformation and Java wrappers are both

viable tools– we had more success with wrapping legacy software

transformations– preferred choice depends on availability of

documentation and test procedures

• Issues not addressed– economic tradeoffs

• module size vs value of conversion• is the size and function worth the trouble?

– registries and dynamic discovery/integration

Documents

Adapting Legacy Computational Software for XMSF 1 © 2003 White & Pullen, GMU03F-SIW-112 Adapting Legacy Computational Software for XMSF Elizabeth L. White