| <html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>3.2. Parameter passing at Graph Transformation Rules</title><link href="style.css" rel="stylesheet" type="text/css"><meta content="DocBook XSL Stylesheets V1.72.0" name="generator"><link rel="start" href="index.html" title="The VIATRA2 Model Transformation Framework"><link rel="up" href="sec_GraphTransformations.html" title="3. Graph Transformation Rules"><link rel="prev" href="def_GTRuleDef.html" title="3.1.1. Graph Transformation Rule Definition"><link rel="next" href="sec_GTRuleBehaviour.html" title="3.3. Behavioural Specification of Graph Transformation Rules"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">3.2. Parameter passing at Graph Transformation Rules</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="def_GTRuleDef.html">Prev</a> </td><th align="center" width="60%">3. Graph Transformation Rules</th><td align="right" width="20%"> <a accesskey="n" href="sec_GTRuleBehaviour.html">Next</a></td></tr></table><hr></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sec_GTParamPass"></a>3.2. Parameter passing at Graph Transformation Rules</h3></div></div></div><p> | |
| Information flow between graph transformation rules and their precondition and postcondition patterns is carried | |
| out by parameter passing. | |
| </p><p> | |
| Like in case of ASM rules, formal parameters of graph transformation rules can be grouped into three categories. | |
| Note that this categorization is independent from the fact whether a given parameter is bound or unbound when | |
| applying a GT rule. | |
| </p><div class="itemizedlist"><ul type="disc"><li><p> | |
| <span class="emphasis"><em>in</em></span>: The values of | |
| <span class="strong"><strong>input parameters</strong></span> | |
| <a name="N10D39" class="indexterm"></a> | |
| passed to a graph transformation rule will be restored after applying the rule, i.e. if a new value is | |
| assigned to an input variable during the application of a GT rule, this value will no longer be visible | |
| after rule application. Its typical usage is that an initial match of a GT rule is assigned this way. | |
| </p><p>It is a run-time error if an input parameter is unbound when calling a GT rule.</p></li><li><p> | |
| <span class="emphasis"><em>out</em></span>: The values of | |
| <span class="strong"><strong>output parameters</strong></span> | |
| <a name="N10D4C" class="indexterm"></a> | |
| passed to a graph transformation rule will be ignored when initiating pattern matching for the | |
| precondition pattern, i.e. these parameters are treated during pattern matching as if they were unbound. | |
| However, these values are passed back to the caller environment to make the new values accessible. | |
| </p></li><li><p> | |
| <span class="emphasis"><em>inout</em></span>: The values of | |
| <span class="strong"><strong>inout parameters</strong></span> | |
| <a name="N10D5D" class="indexterm"></a> | |
| of a graph transformation rule are passed to a graph pattern matching engine (as in case of | |
| <span class="strong"><strong>input parameters</strong></span>), and they are also passed back to the caller environment | |
| (as in case of <span class="strong"><strong>output parameters</strong></span>). | |
| </p><p>It is a run-time error if an input parameter is unbound when calling a GT rule.</p></li></ul></div><p> | |
| Note that this interpretation of input and output variables is a change from previous release, where input and | |
| output parameters of a GT rule were interpreted after the pattern matching phase. | |
| </p><p> | |
| As illustrated by <a href="sec_GTParamPass.html#fig:VTCL_ParamRelations" title="Figure 2.2. Relations of parameters of the parts of a GT rule">Figure 2.2, “Relations of parameters of the parts of a GT rule”</a>, a parameter of a graph transformation rule can be used | |
| (i) in the precondition pattern, (ii) in the postcondition pattern, or in the action part (or in any combination of these) | |
| provided that they are listed in the parameter list(s) of the corresponding patterns. In case of the action part, all | |
| parameters of the GT rule itself of the precondition and postcondition patterns can be used (i.e. all these | |
| variables are part of an implicit parameter list of the action part). | |
| </p><div class="figure"><a name="fig:VTCL_ParamRelations"></a><p class="title"><b>Figure 2.2. Relations of parameters of the parts of a GT rule</b></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="images/others/ParamRelations.png" align="middle" width="500" alt="Relations of parameters of the parts of a GT rule"></div></div><p></p></div><br class="figure-break"><div class="itemizedlist"><ul type="disc"><li><p> | |
| Bound parameters of the precondition pattern are called | |
| <span class="emphasis"><em>input parameters of the precondition</em></span>, | |
| while unbound parameters of the postcondition are called | |
| <span class="emphasis"><em>output parameters of the precondition</em></span>. | |
| Input parameters are either parameters of the precondition pattern, | |
| or they are <span class="emphasis"><em>input</em></span> | |
| or <span class="emphasis"><em>inout</em></span> | |
| parameters of the GT rule itself. | |
| </p></li><li><p> | |
| Bound parameters of the postcondition pattern are called | |
| <span class="emphasis"><em>input parameters of the postcondition</em></span>, | |
| while unbound parameters of the postcondition are called | |
| <span class="emphasis"><em>output parameters of the precondition</em></span>. | |
| Input parameters are <span class="emphasis"><em>input</em></span> or <span class="emphasis"><em>inout</em></span> | |
| parameters of the GT rule itself. | |
| </p></li></ul></div><p> | |
| In the rare case when values are assigned multiple times to the same output parameter, assignments in the | |
| precondition pattern are overridden by assignments defined by the postcondition pattern, which, in turn, are | |
| overridden by assignments in the action part. | |
| </p></div><div class="navfooter"><hr><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="def_GTRuleDef.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="sec_GraphTransformations.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="sec_GTRuleBehaviour.html">Next</a></td></tr><tr><td valign="top" align="left" width="40%">3.1.1. Graph Transformation Rule Definition </td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td valign="top" align="right" width="40%"> 3.3. Behavioural Specification of Graph Transformation Rules</td></tr></table></div></body></html> |