adapting legacy computational software for xmsf

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

white@cs.gmu.edu; mpullen@gmu.edu

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

Overview

• Background

• Web services, XML and SOAP

• From legacy code to web services

• Experiments to date

• Conclusions

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

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.

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

Background - Goals

Enable use of legacy code in XMSF:

• Approach should be easy to apply

• Platform independence

• Inexpensive or freely available tools

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

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

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

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.

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

Web Services Model

Service Provider

Service Provider

Service Consumer

Service Consumer

Service RegistryService

Registry

Bind

Publish Query

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

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

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

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.

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

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

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

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

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

Java-Based Web services

ServiceConsumer

ServiceProvider

LegacyCode

SOAPMessages

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

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

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

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

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

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

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

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.

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

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

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

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