--                         <b>return</b> STD.STANDARD.BIT];
     -- <b>alias</b> "nor"  <b>is</b> STD.STANDARD."nor"
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BIT];
     -- <b>alias</b> "xor" <b>is</b> STD.STANDARD."xor"
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BIT];
     -- <b>alias</b> "xnor <b>is</b> STD.STANDARD."xnor"
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BIT];
     -- <b>alias</b> "not" <b>is</b> STD.STANDARD."not"
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BIT];
     -- <b>alias</b> "="   <b>is</b> STD.STANDARD."="
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BOOLEAN];
     -- <b>alias</b> "/="  <b>is</b> STD.STANDARD."/="
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BOOLEAN];
     -- <b>alias</b> "&lt;"   <b>is</b> STD.STANDARD."&lt;"
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BOOLEAN];
     -- <b>alias</b> "&lt;="  <b>is</b> STD.STANDARD."&lt;="
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BOOLEAN];
     -- <b>alias</b> ">"  <b>is</b> STD.STANDARD.">"
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BOOLEAN];
     -- <b>alias</b> ">="  <b>is</b> STD.STANDARD.">="
     --                     [STD.STANDARD.BIT, STD.STANDARD.BIT
     --                         <b>return</b> STD.STANDARD.BOOLEAN];
</pre>
<p>NOTE--An alias of an explicitly declared object is not an explicitly declared object,nor is the alias of a subelement or slice of an explicitly declared object an explicitly declared object.
<h2><a name="4.4">  <a href = "1076_4.HTM#4.4"> 4.4 </a>   Attribute declarations</a></h2>
<p>An attribute is a value, function, type, range, signal, or constant that may be associated with one or more named entities in a description.  There are two categories of attributes: predefined attributes and user-defined attributes.  Predefined attributes provide information about named entities in a description.  Section 14 contains the definition of all predefined attributes.  Predefined attributes that are signals may not be updated.
<p>User-defined attributes are constants of arbitrary type.  Such attributes are defined by an attribute declaration.
<pre>     attribute_declaration ::=
          <b>attribute</b> identifier: type_mark ;
</pre>
<p>The identifier is said to be the <i>designator</i> of the attribute.  An attribute may be associated with an entity declaration, an architecture, a configuration,a procedure, a function, a package, a type, a subtype, a constant, a signal, a variable, a component, a label, a literal, a unit, a group, or a file.
<p>The type mark must denote a subtype that is neither an access type nor a file type.  The subtype need not be constrained.
<p><i>Examples:</i>
<pre>     <b>type</b> COORDINATE <b>is</b> <b>record</b> X,Y: INTEGER; <b>end</b> <b>record</b>;
     <b>subtype</b> POSITIVE <b>is</b> INTEGER <b>range</b> 1 <b>to</b> INTEGER'HIGH;
     <b>attribute</b> LOCATION: COORDINATE;
     <b>attribute</b> PIN_NO: POSITIVE;

</pre>
<h4>NOTES</h4>
<p>1--A given named entity E will be decorated with the user-defined attribute A if and only if an attribute specification for the value of attribute A exists in the same declarative part as the declaration of E.  In the absence of such a specification, an attribute name of the form E'A is illegal.
<p>2--A user-defined attribute is associated with the named entity denoted by the name specified in a declaration, not with the name itself.  Hence, an attribute of an object can be referenced by using an alias for that object rather than the declared name of the object as the prefix of the attribute name, and the attribute referenced in such a way is the same attribute (and therefore has the same value) as the attribute referenced by using the declared name of the object as the prefix.
<p>3--A user-defined attribute of a port, signal, variable, or constant of some composite type is an attribute of the entire port, signal, variable, or constant, not of its elements.  If it is necessary to associate an attribute with each element of some composite object, then the attribute itself can be declared to be of a composite type such that for each element of the object,there is a corresponding element of the attribute.
<h2><a name="4.5">  <a href = "1076_4.HTM#4.5"> 4.5 </a>   Component declarations</a></h2>
<p>A component declaration declares a virtual design entity interface that may be used in a component instantiation statement.  A component configuration or a configuration specification can be used to associate a component instance with a design entity that resides in a library.
<pre>     component_declaration ::=
        <b>component</b> identifier [ <b>is</b> ]
           [ <i>local</i>_generic_clause ]
           [ <i>local</i>_port_clause ]
        <b>end component</b> [ <i>component</i>_simple_name ] ;
</pre>
<p>Each interface object in the local generic clause declares a local generic.  Each interface object in the local port clause declares a local port.
<p>If a simple name appears at the end of a component declaration, it must repeat the identifier of the component declaration.
<h2><a name="4.6">  <a href = "1076_4.HTM#4.6"> 4.6 </a>   Group template declarations</a></h2>
<p>A group template declaration declares a <i>group template</i>, which defines the allowable classes of named entities that can appear in a group.
<pre>     group_template_declaration ::=
         <b>group</b> identifier <b>is</b> ( entity_class_entry_list ) ;

     entity_class_entry_list ::=
         entity_class_entry { , entity_class_entry }

     entity_class_entry ::=  entity_class [ &lt;> ]
</pre>
<p>A group template is characterized by the number of entity class entries and the entity class at each position.  Entity classes are described in   <a href = "1076_5.HTM#5.1"> 5.1 </a>  .
<p>An entity class entry that is an entity class defines the entity class that may appear at that position in the group type.  An entity class entry that includes a box (&lt;>) allows zero or more group constituents to appear in this position in the corresponding group declaration; such an entity class entry must be the last one within the entity class entry list.
<p><i>Examples:</i>
<pre>     <b>group</b> PIN2PIN <b>is</b> (<b>signal</b>, <b>signal</b>);         --  Groups of this type consist of two signals.

     <b>group</b> RESOURCE <b>is</b> (<b>label</b> &lt;>);              --  Groups of this type consist of any number 
                                                --  of labels.
     <b>group</b> DIFF_CYCLES <b>is</b> (<b>group</b> &lt;>);           --  A group of groups.
</pre>
<h2><a name="4.7">  <a href = "1076_4.HTM#4.7"> 4.7 </a>   Group declarations</a></h2>
<p>A group declaration declares a <i>group</i>, a named collection of named entities.  Named entities are described
<p>in   <a href = "1076_5.HTM#5.1"> 5.1 </a>  .
<pre>     group_declaration ::=
         <b>group</b> identifier : <i>group_template</i>_name ( group_constituent_list ) ;

     group_constituent_list ::=  group_constituent { , group_constituent }

     group_constituent ::=  name | character_literal
</pre>
<p>It is an error if the class of any group constituent in the group constituent list is not the same as the class specified by the corresponding entity class entry in the entity class entry list of the group template.
<p>A name that is a group constituent may not be an attribute name (see   <a href = "1076_6.HTM#6.6"> 6.6 </a>  ), nor, if it contains a prefix, may that prefix be a function call.
<p>If a group declaration appears within a package body, and a group constituent within that group declaration is the same as the simple name of the package body, then the group constituent denotes the package declaration and not the package body.  The same rule holds for group declarations appearing within subprogram bodies containing group constituents with the same designator as that of the enclosing subprogram body.
<p>If a group declaration contains a group constituent that denotes a variable of an access type, the group declaration declares a group incorporating the variable itself, and not the designated object, if any.
<p><i>Examples:</i>
<pre>     <b>group</b> G1: RESOURCE (L1, L2);                    --  A group of two labels.

     <b>group</b> G2: RESOURCE (L3, L4, L5);                --  A group  of three labels.

     <b>group</b> C2Q: PIN2PIN (PROJECT.GLOBALS.CK, Q);     --  Groups may associate named
                                                     --  entities in different declarative                             --  parts (and regions).
     <b>group</b> CONSTRAINT1: DIFF_CYCLES (G1, G3);        --  A group of groups.
</pre>
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