<html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>1.1.3.&nbsp;Namespace Import</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_VtclFile.html" title="1.1.&nbsp;VTCL Files"><link rel="prev" href="def_NamespaceDefinition.html" title="1.1.2.&nbsp;Namespace Definition"><link rel="next" href="sec_MachineDefinition.html" title="1.2.&nbsp;Machine Definition"></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">1.1.3.&nbsp;Namespace Import</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="def_NamespaceDefinition.html">Prev</a>&nbsp;</td><th align="center" width="60%">1.1.&nbsp;VTCL Files</th><td align="right" width="20%">&nbsp;<a accesskey="n" href="sec_MachineDefinition.html">Next</a></td></tr></table><hr></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="def_NamespaceImport"></a>1.1.3.&nbsp;Namespace Import</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_NamespaceImport_Description"></a>Description</th></tr><tr><td valign="top" align="left"><p>
  A <span class="strong"><strong>namespace import</strong></span><a name="N10161" class="indexterm"></a> 
  is  part of a <a href="def_VtclFile.html" title="1.1.1.&nbsp;VTCL file">VTCL file</a>; it
  makes typing of model elements easier since the elements of the model subtree
  determined by the namespace can be referenced relative to the namespace 
  when using them as types.
		</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_NamespaceImport_Syntax"></a>Syntax</th></tr><tr><td valign="top" align="left"><p>
			<pre class="programlisting">
NamespaceImportsAST ::= $empty 
                      | NamespaceImportsAST NamespaceImportAST
NamespaceImportAST ::= <span class="token">import</span> <a href="def_ModelElementName.html" title="5.7.1.&nbsp;Model Element Name">QualifiedTypeNameAST</a> <span class="token">;</span>
			</pre>
		</p><p>
    Namespaces are identified by <a href="def_ModelElementName.html" title="5.7.1.&nbsp;Model Element Name">qualified model element names</a>.

    Import instructions must be placed at the beginning of the file.
		</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_NamespaceImport_Semantics"></a>Semantics</th></tr><tr><td valign="top" align="left"><p>
    The result of importing a namespace to a file is that all model elements
    defined in or below the model element identified by the namespace can be
    referenced inside of all the machines defined in the given file with their
    local names or qualified names local to the given namespace.
		</p><p>
				Namespace imports can result name clashes:
				<div class="itemizedlist"><ul type="disc"><li><p>between a locally defined and an imported name, or</p></li><li><p>between two imported names.</p></li></ul></div>
		</p><p>
      In the first case local (short) name always refers to the locally defined
      element (entity, relation, function, variable, rule etc.), whereas the
      imported element can be referred by its fully qualified name. In
      addition a compile-time warning is issued when a namespace is
      imported that has a conflicting element with a local name.
		</p><p>
      When two different imported namespace contains elements with the same
      name then these elements can be referred by their fully qualified names.
      A compile-time error occurs when such an element is referred by its local
      name.
		</p><p>
      A name clash can occur between a locally defined element and an element
      in the root namespace; in this case root element can be reached, but the
      element in the imported name space not. In this case a warning is issued by
      the compiler.
		</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_NamespaceImport_Constraints"></a>Constraints</th></tr><tr><td valign="top" align="left"><p>
  Only an entity identifies a namespace in the model space, i.e. the
  <a href="def_ModelElementName.html" title="5.7.1.&nbsp;Model Element Name">qualified model element name</a> of the import cannot be the name of a relation.
  	</p></td></tr></table></div><div class="example"><a name="def_NamespaceImport_Example"></a><p class="title"><b>Example&nbsp;2.1.&nbsp;Sample namespace import</b></p><div class="example-contents"><p>
			<pre class="programlisting">
// All elements below the entity uml2.metamodel will become available as types 			
import uml2.metamodel;

// Now the type uml2.metamodel.Classifier of C can be shortened 
pattern myPattern(C) = {
 Classifier(C);
}			
			</pre>
		</p></div><p></p></div><br class="example-break"><div class="highlights"><a name="def_NamespaceImport_SeeAlso"></a><p><b>See also:&nbsp;</b>
			<a href="def_Entity.html" title="2.2.1.&nbsp;Entity">Entity</a>, <a href="def_Relation.html" title="2.2.2.&nbsp;Relation">Relation</a>
			</p></div></div><div class="navfooter"><hr><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="def_NamespaceDefinition.html">Prev</a>&nbsp;</td><td align="center" width="20%"><a accesskey="u" href="sec_VtclFile.html">Up</a></td><td align="right" width="40%">&nbsp;<a accesskey="n" href="sec_MachineDefinition.html">Next</a></td></tr><tr><td valign="top" align="left" width="40%">1.1.2.&nbsp;Namespace Definition&nbsp;</td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td valign="top" align="right" width="40%">&nbsp;1.2.&nbsp;Machine Definition</td></tr></table></div></body></html>