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XQuery Engine Prototype : Coalition Theatre Logistics (CTL) : Advanced Concept Technology Demonstrator (ACTD)

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Abstract

During the architectural design of the Coalition Theatre Logistics (CTL) Advanced Concept Technology Demonstrator (ACTD) it was identified that a data query capability that operates over XML-based web services was required. This document outlines how a new technology called XQuery could provide this XML-based query capability over web service oriented communication. Also outlined is a possible solution along with a discussion of its limitations and capabilities. A successful implementation of the XQuery engine was developed with performance metrics and architectural designs of the implemented system included within.

Executive Summary

Australia is involved in a joint project called CTL ACTD. The CTL ACTD project is responsible for researching the policy and technical issues with sharing logistic data between multiple nations that operate together in coalition operations. CTL ACTD has three main objectives: 1. Coalition Movement Planning - To provide the ability to plan and monitor movement of troops, equipment and supplies in and out of the Area of Operations (AO). 2. Supply and Sustainment (with In-Transit Visibility (ITV)) - Allow the coalition task commander the ability to plan the supply and sustainment requirements of the coalition force. This objective is also striving to provide ITV feeds to track troops, equipment, and supplies in and out of the AO for plan execution monitoring. 3. Infrastructure Visibility - Allow the Coalition Task Force Commander the ability to view details about infrastructure required to support the logistics of the coalition operation. This includes information about roads, warehouses, airports, seaports, etc. During the architectural design phase of CTL a number of capabilities were identified that require further analysis before integration. One such capability is a query and search component for data exposed by web services. In the CTL architecture all data communication is handled via the use of web services. Web services allow for applications to request data in the form of XML documents. Within the architecture there are numerous web services implemented providing different information or functionality. Some web services allow data to be received for storage in a database, while others allow for particular types of data to be requested. For this XQuery prototype we are only interested in the latter type of web service. In the current CTL architecture when a client requests an XML document it calls a web service to return the required XML. For example if the client is interested in movement requests it would call the movement request web service to return the movement request XML documents. The problem with this method of operation is that the web service does not discriminate and returns all documents it can access. This can lead to extremely large results, even if the client only requires part of the data returned. To constrain the results the client needs to send its selection criteria in its initial request. XQuery could be used to define the criterion. The XQuery Prototype described in this document defines how the XQuery standard can be incorporated with the CTL web services. The XQuery Prototype is implemented as a web service that sits on top of a database allowing the advanced XQuery searching capabilities to be applied to the XML data returned. Data contained in the database is stored in a relational structure while XML documents that XQuery operates on is hierarchical. To support the mapping between the relational and hierarchical structures an additional component was built so that the XQuery statements could be applied. The XQuery enhanced web services then operate by extracting the XML documents using the mapping component and applying the XQuery statement so only required data is returned to the client. Testing performed on the prototype showed that the XQuery Engine is quite fast, and that the relational to hierarchical mapping transformation is the actual bottleneck in the system. More than half of the total time of a query is spent transforming the data and, when there are many records in the database, this ransformation time can become unacceptably high. The tests also revealed that the transformation takes much longer with Oracle than it does with SQL Server databases. Although the relational data to XML transformation took considerable time, this time lag is already present in the current CTL architecture. Therefore the addition of the XQuery capability provides extra functionality with similar performance. The XQuery Prototype successfully demonstrated that XQuery could be used to search and constrain results from web services. With performance improvements the XQuery capability will prove to be a valuable capability for use in CTL or other web service deployments.

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