non-releases/trunk_before_flattening/src/documentation/src/content/xdocs/c21-databases/content_en.html - cocoon - Git at Google

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 <title>Database Access</title>
 <link href="http://purl.org/DC/elements/1.0/" rel="schema.DC">
 <meta content="Christian Haul" name="DC.Creator">
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 <h1>Introduction</h1>

 <p>
     Publishing dynamic content or creating web-applications
     eventually involves database access. Apache Cocoon
     offers a number of different approaches to access
     (object) relational and XML databases. This document provides
     an overview of the different ways to access (object)
     relational databases.
     </p>

 <p>
     This document will not explain how to set up database
     connectivity with Apache Cocoon. For this, see <a href="../../developing/datasources.html">here.</a>

 </p>

 <p>
     Basically, there are three different approaches available:
     <a href="actions.html">Actions,</a> <a href="../xsp/logicsheet-concepts.html">logicsheets,</a>
     and <a href="sitemap.html">transformers.</a> Each approach has
     its pros and cons.
     </p>


 <h1>Actions Approach</h1>

 <p>

 <a href="actions.html">Actions</a> are code to be executed
     during pipeline setup. The outcome of an action can change how a pipeline is
     assembled. For example, a pipeline may produce an alternative
     page to display upon failure of a particular database operation.
     </p>

 <p>
     Actions are especially great for inserting, changing, or deleting data.
     Employing the pipeline-switching features of actions will simplify your
     pages. Such actions are concerned with only one view: either the success
     or failure of an operation.
     </p>

 <p>
     Actions can be useful, even when data is not provided by users.
     For example, you could store tracking information in a database in
     a central location without the need to modify every page.
     </p>

 <p>
     Database actions can read and return data from a database. This is
     useful when the pipeline assembly depends upon such data. It's also
     useful when setting up an environment for XSP processing.
     </p>

 <p>
     Once the database meta data is captured in an XML descriptor file,
     making use of these actions is simply a matter of placing them in a pipeline.
     This is a major advantage of the action approach. No programming is
     required, not even SQL query writing.
     </p>

 <p>
     For more detailed information, read:  <a href="../actions/database-actions.html">Database Actions</a>.
     </p>


 <h1>ESQL Logicsheet Approach</h1>

 <p>
     The use of logicsheets is limited to XSPs. ESQL is currently available
     for Java-based XSPs. Its interface is modeled largely on
     JDBC. Thus, it is advantageous to be familiar with JDBC.
     </p>

 <p>
     ESQL is great when reading data from a database. However, it is less attractive
     to use when it has to react to operation failures. This is due to the fact
     that it adds a layer of complexity to an XSP file, making it
     more difficult to understand and maintain.
     </p>

 <p>
     Complex layouts of the data are easy to achieve. ESQL allows
     the arbitrary nesting of queries and connections. It also provides support for
     stored procedures and complex data types. ESQL provides a means to
     create a structured representation of the database data with a single tag.
     This is useful when generating reports to use
     with other XML-aware software or to be formated with XSL or CSS2.
     XML data can be retrieved from the
     database and included in the output. With some supported database
     management systems, ESQL supports skipping part of the
     resultset as well as limiting the result.
     Given the full power of Java available within XSP,
     any processing of the data is possible.
     </p>

 <p>
     For more detailed information, read:  <a href="../xsp/esql.html">ESQL Taglib</a>.
     </p>


 <h1>SQL Transformer Approach</h1>

 <p>
     An approach using the SQL transformer can be combined with any kind
     of page. This will result in slightly cleaner pages as you don't need
     some of the setup that an ESQL approach requires.
     </p>

 <p>
     On the other hand, it is more or less impossible to react to operation
     failures. This is due to the fact that the pipeline is already assembled
     and the necessary logic to handle such failures is not
     available inside the SQL transformer, unless of course, you are willing
     to write a custom transformer.
     Thus, the transformer approach is best for retrieving data. Creating
     an XML representation of the query result is even simpler than when
     using the ESQL logicsheet. The transformer also supports stored procedures.
     No programming is required, apart from writing SQL.
     </p>

 <p>
     For more detailed information, read: <a href="../transformers/sql-transformer.html">SQL Transformer</a>.
     </p>


 </body>
 </html>
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<head>
	<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
	<title>Database Access</title>
	<link href="http://purl.org/DC/elements/1.0/" rel="schema.DC">
	<meta content="Christian Haul" name="DC.Creator">
	</head>
	<body>


	<h1>Introduction</h1>

	<p>
	Publishing dynamic content or creating web-applications
	eventually involves database access. Apache Cocoon
	offers a number of different approaches to access
	(object) relational and XML databases. This document provides
	an overview of the different ways to access (object)
	relational databases.
	</p>

	<p>
	This document will not explain how to set up database
	connectivity with Apache Cocoon. For this, see <a href="../../developing/datasources.html">here.</a>

	</p>

	<p>
	Basically, there are three different approaches available:
	<a href="actions.html">Actions,</a> <a href="../xsp/logicsheet-concepts.html">logicsheets,</a>
	and <a href="sitemap.html">transformers.</a> Each approach has
	its pros and cons.
	</p>



	<h1>Actions Approach</h1>

	<p>

	<a href="actions.html">Actions</a> are code to be executed
	during pipeline setup. The outcome of an action can change how a pipeline is
	assembled. For example, a pipeline may produce an alternative
	page to display upon failure of a particular database operation.
	</p>

	<p>
	Actions are especially great for inserting, changing, or deleting data.
	Employing the pipeline-switching features of actions will simplify your
	pages. Such actions are concerned with only one view: either the success
	or failure of an operation.
	</p>

	<p>
	Actions can be useful, even when data is not provided by users.
	For example, you could store tracking information in a database in
	a central location without the need to modify every page.
	</p>

	<p>
	Database actions can read and return data from a database. This is
	useful when the pipeline assembly depends upon such data. It's also
	useful when setting up an environment for XSP processing.
	</p>

	<p>
	Once the database meta data is captured in an XML descriptor file,
	making use of these actions is simply a matter of placing them in a pipeline.
	This is a major advantage of the action approach. No programming is
	required, not even SQL query writing.
	</p>

	<p>
	For more detailed information, read: <a href="../actions/database-actions.html">Database Actions</a>.
	</p>



	<h1>ESQL Logicsheet Approach</h1>

	<p>
	The use of logicsheets is limited to XSPs. ESQL is currently available
	for Java-based XSPs. Its interface is modeled largely on
	JDBC. Thus, it is advantageous to be familiar with JDBC.
	</p>

	<p>
	ESQL is great when reading data from a database. However, it is less attractive
	to use when it has to react to operation failures. This is due to the fact
	that it adds a layer of complexity to an XSP file, making it
	more difficult to understand and maintain.
	</p>

	<p>
	Complex layouts of the data are easy to achieve. ESQL allows
	the arbitrary nesting of queries and connections. It also provides support for
	stored procedures and complex data types. ESQL provides a means to
	create a structured representation of the database data with a single tag.
	This is useful when generating reports to use
	with other XML-aware software or to be formated with XSL or CSS2.
	XML data can be retrieved from the
	database and included in the output. With some supported database
	management systems, ESQL supports skipping part of the
	resultset as well as limiting the result.
	Given the full power of Java available within XSP,
	any processing of the data is possible.
	</p>

	<p>
	For more detailed information, read: <a href="../xsp/esql.html">ESQL Taglib</a>.
	</p>



	<h1>SQL Transformer Approach</h1>

	<p>
	An approach using the SQL transformer can be combined with any kind
	of page. This will result in slightly cleaner pages as you don't need
	some of the setup that an ESQL approach requires.
	</p>

	<p>
	On the other hand, it is more or less impossible to react to operation
	failures. This is due to the fact that the pipeline is already assembled
	and the necessary logic to handle such failures is not
	available inside the SQL transformer, unless of course, you are willing
	to write a custom transformer.
	Thus, the transformer approach is best for retrieving data. Creating
	an XML representation of the query result is even simpler than when
	using the ESQL logicsheet. The transformer also supports stored procedures.
	No programming is required, apart from writing SQL.
	</p>

	<p>
	For more detailed information, read: <a href="../transformers/sql-transformer.html">SQL Transformer</a>.
	</p>



	</body>
	</html>