1 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL: An XML-based Scripting Language for Workflow Execution in a Grid Environment Networking and Distributed Systems Carla S. Hunt and Clayton S. Ferner Department of Computer Science Jeffrey L. Brown Department of Mathematics University of North Carolina at Wilmington

2 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Presentation Contents: Introduction Motivation for JXPL Characteristics from the Lisp language that influenced JXPL's design The role of XML Syntax including a grammar for JXPL in Extended Backus-Naur Form (EBNF) Specifics about some of JXPL's functions Conclusions, current and future work

3 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Introduction: Grid Computing Offers users access to computing resources such as processing cycles, software, data storage, etc., in a seamless environment Also offers universities,corporations and other organizations a way to make better use of under-utilized resources Grid computing technologies are still emerging; one area of research is user interface development including grid portals and workflow editors

4 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Introduction: GridNexus An example of a workflow editor A graphical user interface capable of integrating web and grid services into a workflow Generates JXPL scripts to describe graphical workflows, which can then be executed by a JXPL interpreter

5 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Introduction: JXPL A new functional scripting language Uses XML syntax; Lisp-like design A workflow language designed to interact easily with web and grid services Has built in web and grid service clients that can communicate with a variety of web and grid services Not intended to be written by programmers, but generated by applications

6 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Introduction: Purpose of the paper To encourage developers to create applications that generate JXPL as a means of executing scientific workflows capable of interacting with web and grid services To serve as a reference to anyone desiring to create new applications that can produce JXPL

7 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Motivation for JXPL: To separate the graphical component of a workflow editor from both the representation of the workflow as well as the execution of the workflow This separation simplifies the implementation of the GUI Allows workflows to be executed on processors other than the local processor Makes it possible for other tools besides GridNexus to create JXPL

8 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Motivation for JXPL (Cont): Ability to shield the user from much of the complexity associated with using web and grid services The JXPL interpreter can be invoked via a URI, which allows users to decide where units of work are computed JXPL can manage the interaction between Grid Data Services, which are a special type of Globus Toolkit 3 (GT3) service

9 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL is a functional scripting language with a Lisp-like design In both languages: Everything is either an Atom or a List Lists contain Atoms or other Lists, which allows for nesting of data structures The list data object can be used to define programs, data structures, and functions

10 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL scripts are written in XML The parentheses of Lisp are replaced by more descriptive XML tags Being written in XML, JXPL is compatible with XML-aware programs, protocols and parsers The XML format makes it easy for programs to generate JXPL Representing JXPL objects as XML elements facilitates a high level of abstraction

11 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL scripts are written in XML (Cont) Removing object typing concerns from the programming model is analogous to a pure Lisp implementation providing advantages such as: Ability to nest and evaluate recursively Making it possible to accurately depict dependencies between tasks in a workflow Especially useful in a graphical workflow environment where workflows are naturally nested

12 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL scripts must be well-formed XML documents: Must contain a root element, the JXPL expression Use the namespace, All elements must have closing tags, are case sensitive, must be properly nested, and attribute values must be quoted

13 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Extended Backus-Naur Form (EBNF) for the JXPL language We use the following conventions in the JXPL grammar: x|y means one of either x or y, {x} indicates zero or more occurrences, [x] indicates zero or one occurrence, terminals are underlined and non-terminals are capitalized.

14 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Simple JXPL example to demonstrate the grammar The primitive construct is used to describe a function call This example uses the function named Arithmetic The function is called with one property named operation with a value of multiply and two operands which are the rational numbers 7/5 and 3/11 (A) Multiplication using the JXPL (* 7/5 3/11) (B) Equivalent in Lisp Arithmetic Function

15 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL Simple Types Correspond to Lisp Atoms and include symbols, strings, integers, rationals, decimals and function names No explicit Boolean type; false is an empty list and everything else is true A JXPL symbol (like the Lisp symbol) is a multipurpose element that can legally represent the number ten, the string value “ten”, a function named “ten” or a variable named “ten” There are three defined numeric types: integer, decimal and rational

16 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL Primitives The JXPL primitive is analogous to a function The primitive tag is used to call a function The syntax of a function call with a primitive tag is: properties arguments

17 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL Primitives: Defun Defun is a predefined function that allows users to define their own functions The syntax of Defun is: parameters function body

18 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Using Defun to define the Myadd function (a) Defining the Myadd function (b) Calling the Myadd function

19 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL Primitives: WS Client This function is designed to be a generic function for a web service To use the Web Service Client, the Web- Services Description Language (WSDL) is needed to generate a call to the appropriate method of the web service The arguments to the WS Client are the WSDL, the name of the method of the service to be called, and any arguments needed to call that method

20 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. WS Client Example Below is the JXPL script that is produced for a simple web service called MyMath In this example, the client requests the squared method with an argument of 2 from the MyMath web service, a result of 4 is returned

21 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. WSRF Client Example Below is the JXPL script that is produced for a grid service called MathService

22 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. JXPL Primitives: Prog XML files have a single root element restricting JXPL scripts to a single workflow The Prog function was created so that multiple workflows could be combined into one script The Prog function accepts a list of lists, evaluates each sublist in order and returns the result of evaluating the last list

23 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Conclusions JXPL is an XML-based scripting language inspired by Lisp JXPL is currently used by GridNexus, a graphical workflow editor developed at UNCW Our paper was written to provide a specification for JXPL We wish to encourage others to use JXPL and to create applications that can use JXPL

24 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Conclusions (Cont) JXPL has several nice features: Execution is separate from the graphical interface allowing for batch mode and parallel execution JXPL is based on Lisp making it elegantly simple and easily extensible JXPL uses XML so that it can easily be transmitted using SOAP The JXPL interpreter is written in Java making it easily portable to other platforms

25 IEEE SoutheastCon 2005, April 8-10, 2005, Ft. Lauderdale, Florida. Acknowledgements This work is supported in part by the University of North Carolina Office of the President, UNC Wilmington's Information Technology Systems Division, and the National Science Foundation under Grant No. DBI Questions?