examples/ecore2rdb/index.html

<h1>Henshin Example: Ecore2Rdb</h1>

<p>
<small><i>contributed by Stefan Jurack and Christian Krause</i></small>
</p>

<p>
This is an exogenous transformation for translating an Ecore model to a relational database model. 
This example makes extensive use of nested multi-rules. The purpose of this example is to show how
this concept can be used to construct complex and powerful rules. Note that this example could be
also modeled with simple (but more) rules in Henshin.
</p>

<p>
This example requires Henshin 0.9.3 or higher. The transformation, source code and example input / output models can be found
<a href="http://git.eclipse.org/c/henshin/org.eclipse.emft.henshin.git/tree/plugins/org.eclipse.emf.henshin.examples/src/org/eclipse/emf/henshin/examples/ecore2rdb">here</a>.
</p>

<h2>The Transformation</h2>

<p>
The transformation consist of one main unit and two rules. The main unit is depicted below.
</p>

<p>
<a href="examples/ecore2rdb/main.png"><img src="examples/ecore2rdb/main.png" /></a>
</p>

<p>
The main unit is a sequential unit. It first executes the rule <i>CreateSchema</i> and then the rule
<i>CreateTableInterrelations</i>. The two parameters of the main unit are passed to the <i>CreateSchema</i>
and back again. Note that there is no loop involved: the transformation literally consist of two rule 
application, no matter how large and complex the input model is.
</p>

<p>
The rule <i>CreateSchema</i> is shown in the screenshot below. This rule creates the schema, all tables, and all columns.
In general, the transformation makes use of Henshin's generic <a href="http://wiki.eclipse.org/Henshin_Trace_Model">trace model</a>.
The <i>CreateSchema</i> rule contains the following multi-rules with these tasks:
<ul>
<li><i><b>CreateSchema</i>:</b> Creates a schema for a given package.</li>
<ul>
<li><i><b>tab</b></i>: Creates a table for every class in the parent package.</li>
<ul>
<li><i><b>col</b></i>: Creates a column for every attribute in the parent class.</li>
<ul>
<li><i><b>PKey</b></i>: Marks the columns of ID-attributes as key columns.</li>
</ul>
<li><i><b>newPKey</b></i>: Creates a new key column if there exists no ID-attributes.</li>
</ul>
</ul>
</ul>
</p>

<p>
<a href="examples/ecore2rdb/createSchema.png"><img width="700" src="examples/ecore2rdb/createSchema.png" /></a>
</p>

<p>
The second rule, called <i>CreateTableInterrelations</i>, is shown below.
This rule creates the for all EReferences the corresponding table relations.
For 1..1 references, the rule creates a new column in the table and a foreign key
pointing to the target column. For 1..n references, the rule creates a whole new
table that contains the links.
</p>

<p>
<a href="examples/ecore2rdb/createRelations.png"><img width="700" src="examples/ecore2rdb/createRelations.png" /></a>
</p>


<h2>Example</h2>

<p>
You can find the example Ecore file <i>CarRental.ecore</i> in the same directory. To apply the transformation to this model,
open the file <i>ecore2rdb.henshin</i> in the tree-based Henshin editor. Right-click on the main unit and select <i>Apply Transformation</i>.
In the dialog, click on <i>Browse Workspace</i> and choose the <i>CarRental.ecore</i> file. Now change the parameter type of the
parameter <i>packageName</i> to String and enter <i>CarRentalModel</i> as its value. You can now click on Preview and you should see 
this compare dialog:
</p>

<p>
<a href="examples/ecore2rdb/diff.png"><img width="400" src="examples/ecore2rdb/diff.png" /></a>
</p>

<p>
It shows that the created Schema object and its contents. There is also a new Trace object which could be used to check the 
correspondences between the Ecore and the RDB model. There is also a stand-alone Java application in the example directory
which you can use to execute the transformation programmatically.  
</p>