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* utilities-classes.html |
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* Authors: Michael Daigle |
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* Copyright: 2009 Regents of the University of California and the |
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* National Center for Ecological Analysis and Synthesis |
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* For Details: http://www.nceas.ucsb.edu/ |
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* Created: 2009 January 19 |
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<title>Metacat Utilities Classes</title> |
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<td colspan="7"><div class="title">KNB Software Development Guide: Metacat Utilities Classes</div></td> |
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<tr> |
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<td class="tablehead" colspan="2"><p class="label">Metacat Utilities Classes</p></td> |
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<div class="header1">Table of Contents</div> |
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<div class="toc"> |
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<div class="toc1"><a href="#Overview">Overview</a></div> |
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</div> |
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<a name="Overview"></a><div class="header1">UtiltiesOverview</div> |
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<p>Metacat contains its own utilities classes (as opposed to the utilities classes |
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available in the generic utilities module). These utilities classes provide services |
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that are specific to Metacat. Some of the properties that typify a utility are:</p> |
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<ul> |
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<li>Static methods - all methods are called statically.</li> |
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<li>No state - there are no state variables in a utility.</li> |
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<li>Return UtilException on error - this should be the only checked exception |
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that gets thrown</li> |
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</ul> |
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<p/> If state becomes an issue, you may want to use a service class to provide |
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the functionality you need. See the |
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<a href="./service-base.html">Metacat Service Based Architecture page</a> for more |
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information on services.</p> |
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* metacat-architecture.html |
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* Authors: Michael Daigle |
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* Copyright: 2009 Regents of the University of California and the |
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* National Center for Ecological Analysis and Synthesis |
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* For Details: http://www.nceas.ucsb.edu/ |
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* Created: 2009 January 19 |
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* Version: |
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* |
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<html> |
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<title>Metacat Service Based Architecture</title> |
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user docs directory. This is because the user docs deploy to |
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<body> |
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<td rowspan="2"><img src="./images/KNBLogo.gif"></td> |
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<td colspan="7"><div class="title">KNB Software Development Guide: Metacat Service Based Architecture</div></td> |
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<br> |
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<table width="100%"> |
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<tr> |
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<td class="tablehead" colspan="2"><p class="label">Metacat Service Based Architecture</p></td> |
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<!-- a href="add back file here when one exists" -->Back<!-- /a --> | <a href="./index.html">Home</a> | |
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</table> |
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<div class="header1">Table of Contents</div> |
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<div class="toc"> |
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<div class="toc1"><a href="#Overview">Overview</a></div> |
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<div class="toc1"><a href="#BaseService">Extending BaseService Class</a></div> |
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<div class="toc1"><a href="#ServiceService">Controling Services With ServiceService Class</a></div> |
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</div> |
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<a name="Overview"></a><div class="header1">Overview</div> |
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<p>Metacat is migrating toward a service based architecture. Basically, |
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what this means is that any internal service that Metacat provides should be |
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represented in a singleton class that extends the BaseService class.</p> |
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<p>There are a few basic questions that can be asked when you are creating a |
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class to decide if it should be a service.</p> |
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<ul> |
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<li>Does this class perform some action repeatedly throughout the lifetime of |
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the Metacat application?</li> |
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<li>Does it make sense for this class to cache certain information? This is |
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typically information that is accessed often and seldom changes. For example, |
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system properties rarely change and are constantly being accessed. (Thus the |
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PropertyService class.)</li> |
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<li>Would it make sense for the information in the class to be refreshable? Note |
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that this is not a strict requirement, since, as we will discuss, a class can |
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declare itself to be non-refreshable. A good example of a non-refreshable |
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class might be a database service. If core database information changes, |
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that usually requires a system restart, and not a service refresh.</li> |
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</ul> |
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<p>Any of these could signify the need for a service. Note that another option |
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is to create a utility class. Utility classes are singletons that have static |
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methods and less state requirements. See the |
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<a href="./utilities-classes.html">Utilities Classes page</a> for more information.</p> |
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<a name="BaseService"></a><div class="header1">Extending BaseService Class</div> |
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<p> All Services extend the BaseService class except the ServiceService class (discussed |
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next). </p> |
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<p>Currently, BaseService defines three methods:</p> |
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<ul> |
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<li> refreshable() - a package level abstract method that reports whether the class can be |
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refreshed. This has package level access because we only want ServiceService to be |
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able to access this information. You will need to decide at implementation time |
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whether it makes sense to refresh your service and return the appropriate boolean from |
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this method.</li> |
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<li> doRefresh() - a protected abstract method that performs the service refresh. It is |
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protected because it should only be called by the refresh() method (see next). Typically, |
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an implementation of the doRefresh() method updates any cached values in the service and |
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performs any appropriate state-specific service updates.</li> |
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<li> refresh() - a package level method that calls refreshable() and doRefresh(). It has |
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package level access because we only want the ServiceService to be able to refresh the |
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service</li> |
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</ul> |
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<a name="ServiceService"></a><div class="header1">Controling Services With ServiceService Class</div> |
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<p> The ServiceService class is a exception to the BaseService extension rule. This service |
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controls all other services. It maintains a registry of available services. </p> |
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<p>Some of the methods available via ServiceService are: </p> |
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<ul> |
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<li>registerService() - register a service by sending the service name and an instance of |
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the service. </li> |
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<li>refreshService() - refresh a service by name.</li> |
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</ul> |
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<br> |
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<!-- a href="add back file here when one exists" -->Back<!-- /a --> | <a href="./index.html">Home</a> | |
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<a href="./utilities-classes.html">Next</a> |
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</html> |
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<!-- |
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* sitemaps.html
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* metacat-architecture.html
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* |
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* Authors: Michael Daigle |
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* Copyright: 2008 Regents of the University of California and the |
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* |
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<HTML>
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<TITLE>Metacat Architecture</TITLE>
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<html>
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<head>
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<title>Metacat Architecture</title>
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<!-- unfortunately, we have to look for the common css file in the |
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user docs directory. This is because the user docs deploy to |
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the top level of the metacat docs on the knb web server --> |
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<link rel="stylesheet" type="text/css" href="../user/common.css"> |
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<link rel="stylesheet" type="text/css" href="./default.css"> |
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<BODY> |
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<body> |
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<table class="tabledefault" width="100%"> |
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<tr> |
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<td rowspan="2"><img src="./images/KNBLogo.gif"></td> |
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<td colspan="7"><div class="title">KNB Software Development Guide: Metacat Architecture</div></td> |
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</tr> |
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<tr> |
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<td><a href="/" class="toollink"> KNB Home </a></td> |
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<td><a href="/data.html" class="toollink"> Data </a></td> |
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<td><a href="/people.html" class="toollink"> People </a></td> |
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<td><a href="/informatics" class="toollink"> Informatics </a></td> |
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<td><a href="/biodiversity" class="toollink"> Biocomplexity </a></td> |
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<td><a href="/education" class="toollink"> Education </a></td> |
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<td><a href="/software" class="toollink"> Software </a></td> |
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<table width="100%"> |
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<tr> |
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<td class="tablehead" colspan="2"><p class="label">Metacat Architecture</p></td> |
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</td> |
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</tr> |
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</table> |
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<div class="header1">Table of Contents</div> |
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<div class="toc"> |
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<div class="toc1"><a href="#Overview">Architecture Overview</a></div> |
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<div class="toc1"><a href="#Sections">Architectural Sections</a></div> |
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</div> |
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<a name="Overview"></a><div class="header1">Architecture Overview</div> |
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<p>Metacat is implemented as a Java Servlet, and so communicates using basic |
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HTTP protocol semantics. The figure below shows the basic structure of |
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the Metacat architecture. A well defined interface for inserting, |
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updating, deleting, querying, and transforming (using XSL) XML documents |
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is presented. We would like to add the DOM API as an alternative |
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supported mechanism for interacting with Metacat, but have not yet |
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implemented this functionality. </p> |
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<p><img src="../user/metacat.gif" /></p> |
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<a name="Sections"></a><div class="header1">Architectural Sections</div> |
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<p> Please refer to the following sections for more information on each area. |
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<ul> |
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<li> <a href="./service-base.html">Service Based Architecture</a></li> |
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<li> <a href="./utilities-classes.html">Utilities Classes</a></li> |
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<li> <!-- a href="./managing-properties.html" -->Managing Properties<!-- /a --></li> |
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<li> <!-- a href="./configuration-infrastructure.html" -->Configuration Infrastructure<!-- /a --></li> |
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</ul> |
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<br> |
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<!-- a href="add back file here when one exists" -->Back<!-- /a --> | <a href="./index.html">Home</a> | |
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<a href="./metacat-dev-hardware.html">Next</a> |
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</ul> |
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</HTML> |
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</body> |
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</html> |
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but we have avoided RDBMS specific features in order to maintain portability |
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to other relational databases. |
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</p> |
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<p> |
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Metacat is implemented as a Java Servlet, and so communicates using basic |
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HTTP protocol semantics. The figure below shows the basic structure of |
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the Metacat architecture. A well defined interface for inserting, |
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updating, deleting, querying, and transforming (using XSL) XML documents |
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is presented. We would like to add the DOM API as an alternative |
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supported mechanism for interacting with Metacat, but have not yet |
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implemented this functionality. |
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</p> |
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<p><img src="../user/metacat.gif" /></p> |
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</td> |
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</tr> |
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<tr><td> </td></tr> |
| ... | ... | |
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<td>The pages below provide more detailed descriptions of the |
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various development and architecture subjects involved in Metacat. |
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<ul> |
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<li> <!-- a href="./metacat-architecture.html" -->Metacat Architecture <!-- /a --></li>
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<li> <a href="./metacat-architecture.html">Metacat Architecture </a></li>
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<li> <!-- a href="./metacat-dev-hardware.html" -->Metacat developement hardware requirements <!-- /a --></li> |
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<li> <!-- a href="./metacat-eclipse-project.html" -->Setting up a Metacat Eclipse project <!-- /a --></li> |
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<li> <a href="./building-metacat.html">Building Metacat</a></li> |
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