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<div class="section" id="component-model">
<span id="componentmodel"></span><h1>Component Model<a class="headerlink" href="#component-model" title="Permalink to this headline">¶</a></h1>
<p>PyXB’s component model is the representation of XML schema components as a
complex relation of data objects. Each object class corresponds to one of
the thirteen <a class="reference external" href="www.w3.org/TR/xmlschema-1/index.html#components">XML Schema Components</a>, and names of components
and their properties follow those definitions. All classes specific to the
component model are found in the <a class="reference external" href="api/pyxb.xmlschema.structures-module.html">pyxb.xmlschema.structures</a> module.</p>
<p>The relationships amongst components is depicted in the following diagram.
Composite aggregation generally denotes ownership and shared aggregation
reference, but don’t look for consistency.</p>
<img alt="_images/ComponentModel.jpg" src="_images/ComponentModel.jpg" />
<div class="section" id="component-model-mix-ins">
<h2>Component Model Mix-ins<a class="headerlink" href="#component-model-mix-ins" title="Permalink to this headline">¶</a></h2>
<p>A variety of <a class="reference external" href="maintref.html#mixins"><em>Mix-in classes</em></a> are used to allow common code to be abstracted or
to mark objects as having certain capabilities. These mixins are:</p>
<ul class="simple">
<li><a class="reference external" href="api/pyxb.xmlschema.structures._SchemaComponent_mixin-class.html">_SchemaComponent_mixin</a> marks the object
as being a schema component and holds its
<a class="reference external" href="api/pyxb.namespace-module.html#NamespaceContext">NamespaceContext</a>. It also records relations between
components in a global definition and their clones where those definitions
are expanded.</li>
<li><a class="reference external" href="api/pyxb.xmlschema.structures._Singleton_mixin-class.html">_Singleton_mixin</a> is used to ensure there is only one instance each
of the <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#simple-ur-type-itself">simple ur-type</a> and <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#ur-type-itself">ur-type</a>. It overloads
<tt class="docutils literal"><span class="pre">__new__</span></tt> to ensure that only one instance of the class is ever
constructed.</li>
<li><a class="reference external" href="api/pyxb.xmlschema.structures._Annotated_mixin-class.html">_Annotated_mixin</a> provides the support for all components that
contain an <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#cAnnotations">annotation</a>
as a child element.</li>
<li><a class="reference external" href="api/pyxb.xmlschema.structures._NamedComponent_mixin-class.html">_NamedComponent_mixin</a> supports components
that can be identified by name. This includes the target namespace (which
may be anonymous) if the component is global, and the <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#Complex_Type_Definitions">complex type
definition</a>
that serves as the component’s <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#e-scope">scope</a> when it is local.</li>
<li><a class="reference external" href="api/pyxb.xmlschema.structures._ValueConstraint_mixin-class.html">_ValueConstraint_mixin</a> provides support
for components that have <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#e-value_constraint">value constraints</a> : that is,
provide a default value and optionally require a fixed value.</li>
<li><a class="reference external" href="api/pyxb.xmlschema.structures._ScopedDeclaration_mixin-class.html">_ScopedDeclaration_mixin</a> is used by
<a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#cElement_Declarations">element declarations</a> and <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#Complex_Type_Definitions">complex
type definitions</a> which may be
named but only referenceable within a specific <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#e-scope">scope</a>.</li>
<li><a class="reference external" href="api/pyxb.xmlschema.structures._AttributeWildcard_mixin-class.html">_AttributeWildcard_mixin</a> provides support
for <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#cAttribute_Group_Definitions">attribute group definitions</a> and
<a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#Complex_Type_Definitions">complex type definitions</a>, both of
which allow <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#Wildcards">wildcard</a>
attributes.</li>
</ul>
</div>
<div class="section" id="other-information">
<h2>Other Information<a class="headerlink" href="#other-information" title="Permalink to this headline">¶</a></h2>
<p>Most of the important information about the component model is best obtained
from the <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#components">specification</a> or
from the <a class="reference external" href="api/pyxb.xmlschema.structures-module.html">PyXB component model API</a>.
Tidbits of other relevant information:</p>
<ul class="simple">
<li>An understanding of <a class="reference external" href="arch_namespaces.html#resolution"><em>Namespace Resolution</em></a> is important.</li>
<li>Element and attribute declarations that are incorporated by reference are
represented in local scope by a copy of the global declaration. This aids
in the infrastructure that binds declarations from model and attribute
groups to a specific context. Local declarations are associated only with
the complex type in which they appear; types that extend or restrict that
type refer to the declaration instance associated with the base type.</li>
<li>PyXB strictly enforces the <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#cos-element-consistent">requirement</a> that multiple
element declarations within a complex type be compatible with respect to
type and other attributes. Since occurrence restrictions are associated
with a <a class="reference external" href="http://www.w3.org/TR/xmlschema-1/#cParticle">Particle</a> instance
rather than the declaration, the same element can appear in multiple places
with different multiplicities. Note, though, that the default code
generation module collapses all occurrences of any given element into a
single Python field in the binding.</li>
</ul>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#">Component Model</a><ul>
<li><a class="reference external" href="#component-model-mix-ins">Component Model Mix-ins</a></li>
<li><a class="reference external" href="#other-information">Other Information</a></li>
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