<html><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>A Guide to Forming Bundles</title><meta content="DocBook XSL Stylesheets V1.76.0" name="generator"><link rel="home" href="index.html" title="Virgo Programmer Guide"><link rel="up" href="ch03.html" title="Chapter&nbsp;3.&nbsp;Deployment Architecture"><link rel="prev" href="ch03s03.html" title="Regions"><link rel="next" href="ch04.html" title="Chapter&nbsp;4.&nbsp;Developing Applications"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table summary="Navigation header" width="100%"><tr><td align="left" width="20%"><a accesskey="p" href="ch03s03.html">Prev</a>&nbsp;</td><th align="center" width="60%">&nbsp;</th><td align="right" width="20%">&nbsp;<a accesskey="n" href="ch04.html">Next</a></td></tr></table><hr></div><div class="section" title="A Guide to Forming Bundles"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="architecture-forming-bundles"></a>A Guide to Forming Bundles</h2></div></div></div><p> 
			So what makes an application suitable for deployment on the Virgo Server for Apache Tomcat? Since
			OSGi is at the heart of the VTS, modular applications consisting of
			bundles, which each represent distinct functionality and well-defined boundaries, can
			take maximum advantage of the OSGi container&rsquo;s capabilities. The core ideas behind
			forming bundles require following good software engineering practices: separation of
			concerns, loose coupling, and communication through clear interfaces. In this section,
			we look at a few approaches that you may use to create modular applications for
			Virgo Server for Apache Tomcat deployment. Please consider the following discussion as guidelines and
			not as rules. 
		</p><p> 
			Bundles can be formed along horizontal slices of layering and vertical slices of
			function. The objective is to enable independent development of each bundle and minimize
			the skills required to develop each bundle.
		</p><p> For example, an application could have the following bundles:
				<span class="emphasis"><em>infrastructure</em></span>, <span class="emphasis"><em>domain</em></span>,
				<span class="emphasis"><em>repository</em></span>, <span class="emphasis"><em>service</em></span>, and
			<span class="emphasis"><em>web</em></span> as shown in the following diagram.</p><div class="mediaobject"><img src="images/bundle-dependencies-layers.png"></div><p> Each bundle consists of types appropriate for that layer and exports
			packages and services to be used by other layers. Let&rsquo;s examine each bundle in
			more detail: </p><div class="table"><a name="architecture-forming-bundles-across-layers-table"></a><p class="title"><b>Table&nbsp;3.2.&nbsp;Bundles across layers</b></p><div class="table-contents"><table summary="Bundles across layers" border="1"><colgroup><col><col><col><col><col></colgroup><thead><tr><th>Bundles</th><th>Imported Packages</th><th>Exported Packages</th><th>Consumed Services</th><th>Published Services</th></tr></thead><tbody><tr><td>Infrastructure</td><td>Third-party libraries</td><td>Infrastructure interfaces</td><td>None</td><td>None</td></tr><tr><td>Domain</td><td>Depends: for example, if JPA is used to annotate persistent
								types, then JPA packages.</td><td>Public domain types</td><td>None</td><td>None</td></tr><tr><td>Web</td><td>Domain, Service</td><td>None</td><td>Service beans</td><td>None</td></tr><tr><td>Service</td><td>Domain, Infrastructure, Repository</td><td>Service interfaces</td><td>Repository beans</td><td>Service beans</td></tr><tr><td>Repository</td><td>Domain, Third-party libraries, ORM bundles, etc.</td><td>Repository interfaces</td><td>DataSources, ORM session/entity managers, etc.</td><td>Repository beans</td></tr></tbody></table></div></div><p><br class="table-break"></p><p> Within each layer, you may create bundles for each subsystem representing a vertical
			slice of business functionality. For example, as shown in the following figure, the
			service layer is divided into two bundles each representing separate business
			functions. </p><div class="mediaobject"><img src="images/bundle-dependencies-verticals.png"></div><p> You can similarly separate the repositories, domain classes, and web controllers
			based on the business role they play.</p></div><div class="navfooter"><hr><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="ch03s03.html">Prev</a>&nbsp;</td><td align="center" width="20%"><a accesskey="u" href="ch03.html">Up</a></td><td align="right" width="40%">&nbsp;<a accesskey="n" href="ch04.html">Next</a></td></tr><tr><td valign="top" align="left" width="40%">&nbsp;</td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td valign="top" align="right" width="40%">&nbsp;</td></tr></table></div></body></html>