| <html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>2.1.2. Pattern Body</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="def_GraphPatternDef.html" title="2.1.1. Graph Pattern Definition"><link rel="next" href="def_NegativePattern.html" title="2.1.3. Negative Pattern"></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">2.1.2. Pattern Body</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="def_GraphPatternDef.html">Prev</a> </td><th align="center" width="60%">2.1. Pattern Definition</th><td align="right" width="20%"> <a accesskey="n" href="def_NegativePattern.html">Next</a></td></tr></table><hr></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="def_PatternBody"></a>2.1.2. Pattern Body</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_PatternBody_Description"></a>Description</th></tr><tr><td valign="top" align="left"><p> | |
| <span class="strong"><strong>Pattern body</strong></span> | |
| <a name="N1039A" class="indexterm"></a> | |
| is the basic part of the | |
| <a href="def_GraphPatternDef.html" title="2.1.1. Graph Pattern Definition">graph pattern definition</a>. | |
| It determines a constraint set that identifies a part of the model space. | |
| </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_PatternBody_Syntax"></a>Syntax</th></tr><tr><td valign="top" align="left"><pre class="programlisting"> | |
| PatternBodiesAST ::= PatternBodyAST | |
| | PatternBodiesAST <span class="token">or</span> PatternBodyAST | |
| PatternBodyAST ::= <span class="token">{</span> PatternBodyContentsAST <span class="token">}</span> | |
| PatternBodyContentsAST ::= $empty | |
| | PatternBodyContentsAST PatternBodyContentDefAST | |
| PatternBodyContentDefAST ::= PatternBodyContentAST <span class="token">;</span> | |
| | <span class="token">neg</span> <a href="def_GraphPatternDef.html" title="2.1.1. Graph Pattern Definition">GraphPatternDefAST</a> | |
| PatternBodyContentAST ::= LocalPatternBodyElementAST | |
| | <a href="def_PatternComposition.html" title="2.1.5. Pattern Composition">PatternCompositionAST</a> | |
| | <a href="def_NegativePattern.html" title="2.1.3. Negative Pattern">NegativePatternAST</a> | |
| | <a href="def_PatternVariableAssignment.html" title="2.1.7. Pattern Variable Assignment">PatternVariableAssignmentAST</a> | |
| | <a href="def_CheckCondition.html" title="2.1.8. Check Condition">CheckConditionAST</a> | |
| LocalPatternBodyElementAST ::= ModelElementAST | <a href="def_Relationship.html" title="2.2.3. Relationships">RelationshipAST</a> | |
| ModelElementAST ::= <a href="def_Entity.html" title="2.2.1. Entity">EntityAST</a>| <a href="def_Relation.html" title="2.2.2. Relation">RelationAST</a> | |
| </pre><p> | |
| A <span class="strong"><strong>pattern body</strong></span> | |
| <a name="N103DF" class="indexterm"></a> | |
| mainly consists of <span class="strong"><strong>local pattern body elements</strong></span> | |
| <a name="N103E8" class="indexterm"></a>. These defines the typed structure of the pattern. A | |
| <span class="strong"><strong>local pattern body element</strong></span> | |
| can be either a | |
| <span class="strong"><strong>model element</strong></span> | |
| <a name="N103F5" class="indexterm"></a> | |
| or a | |
| <a href="def_Relationship.html" title="2.2.3. Relationships">relationship</a> | |
| definition between model elements. A | |
| <span class="strong"><strong>model element</strong></span> | |
| is either an | |
| <a href="def_Entity.html" title="2.2.1. Entity">entity</a> | |
| or a | |
| <a href="def_Relation.html" title="2.2.2. Relation">relation</a>. | |
| <span class="strong"><strong>Model element</strong></span> | |
| <a name="N1040E" class="indexterm"></a> | |
| are identified by <a href="def_PatternVariable.html" title="2.1.6. Pattern Variable">pattern variables</a>: | |
| these are either the parameters of the pattern or internal variables. | |
| </p><p> | |
| From a | |
| <span class="strong"><strong>pattern body</strong></span> | |
| <a name="N1041D" class="indexterm"></a>, another graph pattern can be invoked by | |
| <a href="def_PatternComposition.html" title="2.1.5. Pattern Composition">pattern composition</a> | |
| or as a | |
| <a href="def_NegativePattern.html" title="2.1.3. Negative Pattern">negative pattern</a>. | |
| </p><p> | |
| Within a | |
| <span class="strong"><strong>pattern body</strong></span> | |
| the unification of variables can be defined: it is called | |
| <a href="def_PatternVariableAssignment.html" title="2.1.7. Pattern Variable Assignment">pattern variable assignment</a>. | |
| </p><p> | |
| Extra conditions can be states in addition to those that defines the typed structure. These are called | |
| <a href="def_CheckCondition.html" title="2.1.8. Check Condition">check condition</a> | |
| s and are formulated by ASM terms. | |
| </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_PatternBody_Semantics"></a>Semantics</th></tr><tr><td valign="top" align="left"><p> | |
| A pattern body defines a conjunction of constraints which has to be fulfilled by a part of the model space | |
| during pattern matching. | |
| </p><p>The following list of core constraints are interpreted by the pattern matcher:</p><div class="itemizedlist"><ul type="disc"><li><p><code class="computeroutput">entity(E)</code>: pattern variable E should be bound to an entity in the model space;</p></li><li><p><code class="computeroutput">relation(R)</code>: pattern variable R should be bound to a relation in the model space;</p></li><li><p><code class="computeroutput">from(R,X)</code>: relation R should lead from model element X;</p></li><li><p><code class="computeroutput">to(R, X)</code>: relation R should lead into model element X;</p></li><li><p><code class="computeroutput">super(X, Y)</code>: X is a supertype of Y or Y is a subtype of X;</p></li><li><p><code class="computeroutput">type(X, Y)</code>: X is type of Y, or Y is instance of X;</p></li><li><p> | |
| <code class="computeroutput">in(X, Y)</code>: | |
| X is a direct child of Y (Y is the parent of X) in the containment hierarchy of the model space. | |
| </p></li><li><p> | |
| <code class="computeroutput">below(X, Y)</code>: | |
| X is a descendant of Y (Y is an ancestor of X) in the containment hierarchy of the model space. | |
| </p></li></ul></div><p>Here the <code class="computeroutput">super</code> and the <code class="computeroutput">below</code>constraints are transitive. | |
| </p><p> | |
| In case of | |
| <a href="def_PatternComposition.html" title="2.1.5. Pattern Composition">pattern composition</a>, | |
| a predicate representing the invoked pattern is derived as a conjunction of the core constraints of its | |
| body. A <a href="def_NegativePattern.html" title="2.1.3. Negative Pattern">negative pattern</a> | |
| defines negative constraints: the pattern body can match only if none of the negative patterns can be | |
| satisfied. In case of recursion, the fixpoint of the recursive predicate is calculated. | |
| </p><p> | |
| In case of multiple pattern bodies (OR-patterns), a different set of constraints is derived, and one of them | |
| needs to be matched for a successful match of the pattern. | |
| </p><p> | |
| The pattern matching engine implements injective pattern matching, i.e. each pattern variable has to be | |
| bound to different model elements in the model space unless (i) two | |
| <a href="def_PatternVariable.html" title="2.1.6. Pattern Variable">pattern variables</a> | |
| are explicitly assigned to the same model element by | |
| <a href="def_PatternVariableAssignment.html" title="2.1.7. Pattern Variable Assignment">pattern variable assignment</a> or | |
| (ii) both variables appear in as actual parameters of called subpatterns. | |
| </p></td></tr></table></div><div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Caution: Constraints"><tr><td valign="top" align="center" rowspan="2" width="25"><img alt="[Caution]" src="images/caution.png"></td><th align="left"><a name="def_PatternBody_Constraints"></a>Constraints</th></tr><tr><td valign="top" align="left"><p>All variables in the head of the pattern must appear in the pattern body</p><div class="itemizedlist"><ul type="disc"><li><p>locally in a model element, or</p></li><li><p>in a (positive or negative) pattern composition or</p></li><li><p>in a variable assignment or</p></li><li><p>in the check condition,</p></li></ul></div><p> | |
| otherwise a compile-time error is generated. In case of OR-patterns, this rule applies to all pattern | |
| bodies. | |
| </p><p> | |
| This is a significant change wrt. the previous versions of VIATRA where all pattern variables had to appear | |
| locally or in the check condition. | |
| </p><p> | |
| The actual parameters of a pattern composition inside a pattern body are restricted to | |
| <a href="def_PatternVariable.html" title="2.1.6. Pattern Variable">pattern variables</a> | |
| . | |
| </p></td></tr></table></div><div class="example"><a name="def_PatternBody_Example"></a><p class="title"><b>Example 2.3. Overview of pattern body contents</b></p><div class="example-contents"><p> | |
| <pre class="programlisting"> | |
| pattern myPattern(A,B,C,D) = | |
| { | |
| myType(A); // local pattern body element | |
| B = A; // variable assignment | |
| neg find myNestedPattern(C); // negative pattern composition | |
| check (name(B) = D); // check condition | |
| } | |
| </pre> | |
| </p></div><p></p></div><br class="example-break"><div class="highlights"><a name="def_PatternBody_DefinedIn"></a><p><b>Defined In: </b> | |
| <a href="def_GraphPatternDef.html" title="2.1.1. Graph Pattern Definition">graph pattern definition</a> | |
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