May 24, 2004IVOA Interop Meeting1 An AXIS-based Java SkyNode Ramon Williamson NCSA T HE US N ATIONAL V IRTUAL O BSERVATORY

May 24, 2004IVOA Interop Meeting2 Apache Axis Axis is an implementation of the SOAP “Simple Object Axis Protocol” submission to the W3C. Axis is a reliable and stable base on which to implement Java Web Services. Java objects are passed “across” the wire by serializing and deserializing the objects to and from XML. We created a Basic SkyNode to access the ADIL (Astronomical Data Image Library) database using AXIS.

May 24, 2004IVOA Interop Meeting3 Stylesheet Model It was desirable to have an easy mechanism to handle ADQL queries. –Input is SQL92, wanted to convert to PostgreSQL –Wanted to make it extensible to other DBs as well as customizing the results. –Most straightforward method is using XML Stylesheets Create a Stylesheet for SQL Standard – based on ADQL schema –Create added stylesheets that import the standard and overide templates in the standard to behave as desired.

May 24, 2004IVOA Interop Meeting4 Sample DB-specific stylesheet <xsl:stylesheet xmlns=" version="1.0">. SELECT FROM <!-- - Restrict Template --> LIMIT Processing order changed PostgreSQL uses LIMIT not TOP Import SQL92 Stylesheet

May 24, 2004IVOA Interop Meeting5 Connecting Xalan to a Web Service We have created classes for plugging in stylesheets into AXIS’ deserialization mechanism, and these are used in our implementation. We also have created a beta class that allows external parsers to be plugged into an Axis Web Service E.g. Plugging SAVOT into a Axis Web Service to handle VOTables

May 24, 2004IVOA Interop Meeting6 Standardizing the WSDL Small differences in the WSDL can cause large problems with interoperability between Services from different implementations (Axis vs.NET), especially in the area of namespaces. The WSDL should be published as a static document, not autogenerated by the implementation ( We should be working toward having a standard WSDL that imports standard schema to represent standard objects (VOTable, ADQL) Only Service-Specific definitions and objects used within the service that are not standard would be defined within the WSDL.

May 24, 2004IVOA Interop Meeting7 Support for other AXIS- compatible Binding Tools JAXB and Castor could also be used to derive classes that could be used for handling data returns. Current version of VOTable-1.1.xsd creates some difficulties in binding to Java (from latest 1.1 Schema): –

May 24, 2004IVOA Interop Meeting8 The generated class extends String, which can’t be done in Java since String is a final class. Removed the mixed element flag and changing ContentType to simpleContent fixes this problem, creating a valid Java class. – This change has been submitted to the VOTable Working Group for review.

May 24, 2004IVOA Interop Meeting9 What’s Next? Implement a Full SkyNode in Java Provide a configurable toolkit to install a SkyNode Service on an SQL database in Java