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Adapting Legacy Computational Software for XMSF
1
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]
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
2
Overview
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Background
Web services, XML and SOAP
From legacy code to web services
Experiments to date
Conclusions
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
3
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.
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
4
Background - Goals
Enable use of legacy code in XMSF:
• Approach should be easy to apply
• Platform independence
• Inexpensive or freely available tools
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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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
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
6
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.
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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Web Services Model
Bind
Service
Provider
Service
Consumer
Publish
Query
Service
Registry
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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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, XMLbased, application-level protocols now emerging
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
9
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.
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
10
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 oneway transmission routed along a message path
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
11
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
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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Java-Based Web services
Service
Consumer
SOAP
Messages
Service
Provider
Legacy
Code
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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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
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
14
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
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
15
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
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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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.
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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Cannon Example
(Bourg, Physics for Game Developers, O’Reilly, 2001)
© 2003 White & Pullen, GMU
03F-SIW-112
Adapting Legacy Computational Software for XMSF
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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
© 2003 White & Pullen, GMU
03F-SIW-112