| <html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>2.1.1. Graph Pattern Definition</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_PatternDefinition.html" title="2.1. Pattern Definition"><link rel="prev" href="sec_PatternDefinition.html" title="2.1. Pattern Definition"><link rel="next" href="def_PatternBody.html" title="2.1.2. Pattern Body"></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">2.1.1. Graph Pattern Definition</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="sec_PatternDefinition.html">Prev</a> </td><th align="center" width="60%">2.1. Pattern Definition</th><td align="right" width="20%"> <a accesskey="n" href="def_PatternBody.html">Next</a></td></tr></table><hr></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="def_GraphPatternDef"></a>2.1.1. Graph Pattern Definition</h4></div></div></div><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip: Description"><tr><td valign="top" align="center" rowspan="2" width="25"><img alt="[Tip]" src="images/tip.png"></td><th align="left"><a name="def_GraphPatternDef_Description"></a>Description</th></tr><tr><td valign="top" align="left"><p> | |
| A graph pattern is the primary means for querying the model space. Graph patterns provide a way for defining | |
| logic constraints for the model structure. | |
| </p><p> | |
| Graph patterns can be either | |
| <span class="emphasis"><em>predefined</em></span> | |
| in the context of a | |
| <a href="def_Machine.html" title="1.2.1. GTASM Machine Definition">GTASM machine</a> | |
| or defined locally as part of a graph transformation rule | |
| <a href="def_GTRuleDef.html" title="3.1.1. Graph Transformation Rule Definition">GT rule</a> | |
| or as part of a negative pattern | |
| <a href="def_NegativePattern.html" title="2.1.3. Negative Pattern">negative pattern</a> | |
| in the body of another pattern. | |
| </p></td></tr></table></div><div class="important" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Important: Syntax"><tr><td valign="top" align="center" rowspan="2" width="25"><img alt="[Important]" src="images/important.png"></td><th align="left"><a name="def_GraphPatternDef_Syntax"></a>Syntax</th></tr><tr><td valign="top" align="left"><pre class="programlisting"> | |
| GraphPatternDefAST ::= <a href="def_Annotation.html" title="1.2.2. Annotation">OptAnnotationsAST</a> <span class="token">pattern</span> <a href="def_ModelElementName.html" title="5.7.1. Model Element Name">TypeNameAST</a> <a href="def_FormalParameter.html" title="5.8.1. Formal Parameters">FormalParameterDefAST</a> <span class="token">=</span> <a href="def_PatternBody.html" title="2.1.2. Pattern Body">PatternBodiesAST</a> | |
| FormalParameterDefAST ::= <span class="token">(</span> <a href="def_FormalParameter.html" title="5.8.1. Formal Parameters">FormalParamsAST</a> <span class="token">)</span> | |
| | <span class="token">(</span> <span class="token">)</span> | |
| </pre><p> | |
| <a href="def_ModelElementName.html" title="5.7.1. Model Element Name">name</a> | |
| is the identifier of the pattern. | |
| </p><p> | |
| The list of | |
| <a href="def_FormalParameter.html" title="5.8.1. Formal Parameters">formal parameters</a> | |
| in graph patterns are different from that of ASM rules in the sense that the parameters of a graph pattern | |
| do not have directions (<code class="computeroutput">in</code>, | |
| <code class="computeroutput">out</code>, | |
| <code class="computeroutput">inout</code>). | |
| </p><p> | |
| A graph pattern definition consists of at least one | |
| <a href="def_PatternBody.html" title="2.1.2. Pattern Body">pattern body</a> | |
| definition. If multiple bodies are present, there is an OR condition between them. | |
| </p></td></tr></table></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note: Semantics"><tr><td valign="top" align="center" rowspan="2" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left"><a name="def_GraphPatternDef_Semantics"></a>Semantics</th></tr><tr><td valign="top" align="left"><p> | |
| A graph pattern can be interpreted as a predefined query evaluated over the model space. Formally (see Sec.~ | |
| ), the semantics of a graph pattern is defined as the set of all matches in the model space. | |
| </p><p> | |
| As graph pattern matching is initiated in an ASM program by a | |
| <a href="def_ChooseRule.html" title="4.3.6. Choose Rule">choose rule</a> | |
| <a name="N10351" class="indexterm"></a> | |
| or | |
| <a href="def_ForallRule.html" title="4.3.7. Forall Rule">forall rule</a> | |
| <a name="N1035A" class="indexterm"></a>, the calling environment may restrict the result set by (i) supplying input parameters, (ii) quantifying | |
| pattern variables existentially or universally, or (iii) setting containment constraints to (the domains of) | |
| pattern variables. | |
| </p><p> | |
| The direction (or adornment) of a pattern parameter is determined only at execution time when pattern | |
| matching is initiated for that pattern. In this way, the same pattern can be called with different settings | |
| for parameter directions at various parts of a VTCL program. | |
| </p><p> | |
| The pattern matching engine implements injective pattern matching, i.e. each pattern variable has to be | |
| bound to different elements in the model (with the single exception of | |
| <a href="def_PatternVariableAssignment.html" title="2.1.7. Pattern Variable Assignment">pattern variable assignment</a>). | |
| </p><p> | |
| If multiple bodies are present (OR-pattern) the pattern is considered to be matched if at least one of the | |
| bodies can be matched. | |
| </p></td></tr></table></div><div class="highlights"><a name="def_GraphPatternDef_DefinedIn"></a><p><b>Defined In: </b> | |
| <a href="def_Machine.html" title="1.2.1. GTASM Machine Definition">GTASM machine</a>, | |
| <a href="def_GTRuleDef.html" title="3.1.1. Graph Transformation Rule Definition">GT rule definition</a> , | |
| <a href="def_NegativePattern.html" title="2.1.3. Negative Pattern">negative pattern</a> | |
| </p></div><div class="highlights"><a name="def_GraphPatternDef_UsedBy"></a><p><b>Used By: </b> | |
| <a href="def_ChooseRule.html" title="4.3.6. Choose Rule">Choose rule</a>, | |
| <a href="def_ForallRule.html" title="4.3.7. Forall Rule">Forall rule</a>, | |
| </p></div></div><div class="navfooter"><hr><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="sec_PatternDefinition.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="sec_PatternDefinition.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="def_PatternBody.html">Next</a></td></tr><tr><td valign="top" align="left" width="40%">2.1. Pattern Definition </td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td valign="top" align="right" width="40%"> 2.1.2. Pattern Body</td></tr></table></div></body></html> |