Docs for schema item link in Chemical Markup Language (CML)

An internal or external link to other objects. Semantics are similar to XLink, but simpler and only a subset is implemented. This is intended to make the instances easy to create and read, and software relatively easy to implement. The architecture is: A single element (link) used for all linking purposes. The link types are determined by the type attribute and can be:. locator. This points to a single target and must carry either a ref or href attribute. locator links are usually children of an extended link. arc. This is a 1:1 link with both ends (from and to) defined. extended. This is usually a parent of several locator links and serves to create a grouping of link ends (i.e. a list of references in documents). Many-many links can be built up from arcs linking extended elements All links can have optional role attributes. The semantics of this are not defined; you are encouraged to use a URI as described in the XLink specification. There are two address spaces: The href attribute on locators behaves in the same way as href in HTML and is of type xsd:anyURI. Its primary use is to use XPointer to reference elements outside the document. The ref attribute on locators and the from and to attributes on arcs refer to IDs (without the '#' syntax). Note: several other specific linking mechanisms are defined elsewhere in STM. relatedEntry should be used in dictionaries, and dictRef should be used to link to dictionaries. There are no required uses of link in STMML but we have used it to map atoms, electrons and bonds in reactions in CML Relation to XLink. At present (2002) we are not aware of generic XLink processors from which we would benefit, so the complete implementation brings little extra value. Among the simplifications from Xlink are: type supports only extended, locator and arc label is not supported and ids are used as targets of links. show and actuate are not supported. xlink:title is not supported (all STM elements can have a title attribute). xlink:role supports any string (i.e. does not have to be a namespaced resource). This mechanism can, of course, still be used and we shall promote it where STM benefits from it The to and from attributes point to IDs rather than labels The xlink namespace is not used It is not intended to create independent linkbases, although some collections of links may have this property and stand outside the documents they link to

<xsd:element name="link" id="el.link"> <xsd:annotation> <xsd:documentation> <h:div class="summary" xmlns:h="http://www.w3.org/1999/xhtml">An internal or external link to other objects.</h:div> <h:div class="description" xmlns:h="http://www.w3.org/1999/xhtml"> <h:p> <h:b>Semantics are similar to XLink, but simpler and only a subset is implemented.</h:b> This is intended to make the instances easy to create and read, and software relatively easy to implement. The architecture is:</h:p> <h:ul> <h:li> <h:b>A single element (<h:tt>link</h:tt>) used for all linking purposes.</h:b> </h:li> <h:li> <h:b>The link types are determined by the <h:tt>type</h:tt> attribute and can be:</h:b>. <h:ul><h:li><h:b>locator</h:b>. This points to a single target and must carry either a <h:tt>ref</h:tt> or <h:tt>href</h:tt> attribute. <h:tt>locator</h:tt> links are usually children of an extended link. <h:li><h:b>arc</h:b>. This is a 1:1 link with both ends (<h:tt>from</h:tt> and <h:tt>to</h:tt>) defined.</h:li> <h:li> <h:b>extended</h:b>. This is usually a parent of several locator links and serves to create a grouping of link ends (i.e. a list of references in documents).</h:li> Many-many links can be built up from arcs linking extended elements</h:li> </h:ul> <h:p>All links can have optional <h:tt>role</h:tt> attributes. The semantics of this are not defined; you are encouraged to use a URI as described in the XLink specification.</h:p> <h:p>There are two address spaces: </h:p> <h:ul> <h:li>The <h:tt>href</h:tt> attribute on locators behaves in the same way as <h:tt>href</h:tt> in HTML and is of type <h:tt>xsd:anyURI</h:tt>. Its primary use is to use XPointer to reference elements outside the document.</h:li> <h:li>The <h:tt>ref</h:tt> attribute on locators and the <h:tt>from</h:tt> and <h:tt>to</h:tt> attributes on <h:tt>arc</h:tt>s refer to IDs (<h:em>without</h:em> the '#' syntax).</h:li> </h:ul> <h:p>Note: several other specific linking mechanisms are defined elsewhere in STM. <h:a href="el.relatedEntry">relatedEntry</h:a> should be used in dictionaries, and <h:a href="st.dictRef">dictRef</h:a> should be used to link to dictionaries. There are no required uses of <h:tt>link</h:tt> in STMML but we have used it to map atoms, electrons and bonds in reactions in CML</h:p> </h:li> </h:ul> <h:p> <h:b>Relation to XLink</h:b>. At present (2002) we are not aware of generic XLink processors from which we would benefit, so the complete implementation brings little extra value. Among the simplifications from Xlink are:</h:p> <h:ul> <h:li> <h:tt>type</h:tt> supports only <h:tt>extended</h:tt>, <h:tt>locator</h:tt> and <h:tt>arc</h:tt> </h:li> <h:li> <h:tt>label</h:tt> is not supported and <h:tt>id</h:tt>s are used as targets of links.</h:li> <h:li> <h:tt>show</h:tt> and <h:tt>actuate</h:tt> are not supported.</h:li> <h:li> <h:tt>xlink:title</h:tt> is not supported (all STM elements can have a <h:tt>title</h:tt> attribute).</h:li> <h:li> <h:tt>xlink:role</h:tt> supports any string (i.e. does not have to be a namespaced resource). This mechanism can, of course, still be used and we shall promote it where STM benefits from it</h:li> <h:li>The <h:tt>to</h:tt> and <h:tt>from</h:tt> attributes point to IDs rather than labels</h:li> <h:li>The xlink namespace is not used</h:li> <h:li>It is not intended to create independent linkbases, although some collections of links may have this property and stand outside the documents they link to</h:li> </h:ul> </h:div> </xsd:documentation> </xsd:annotation> <xsd:complexType> <xsd:sequence> <xsd:any minOccurs="0" maxOccurs="unbounded" /> </xsd:sequence> <xsd:attributeGroup ref="title" /> <xsd:attributeGroup ref="id" /> <xsd:attributeGroup ref="convention" /> <xsd:attributeGroup ref="dictRef" /> <xsd:attributeGroup ref="from" /> <xsd:attributeGroup ref="to" /> <xsd:attributeGroup ref="ref" /> <xsd:attributeGroup ref="fromType"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The type of the object/element in the 'from' attributes. Requires the objects referenced by the 'from' attributes to have a given elementType. Can be overridden by 'from' attributes in individual links. 2005-06-18: created</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="toType"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The type of the object/element in the 'to' attributes. Requires the objects referenced by the 'to' attributes to have a given elementType. Can be overridden by 'to' attributes in individual links. 2005-06-18: created</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="fromSet"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The set of ids in the base of the link. 2005-06-18: created</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="toSet"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The set of ids in the target of the link. 2005-06-18: created</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="fromContext"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The id of the ancestral element of objects referenced by 'from' attributes. Provides a context for uniquifying the references in the 'from' attributes. Thus atoms referenced by ids should be unique within a given molecule and the id of this could be the 'fromContext'. 2005-06-18: created</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="toContext"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The id of the ancestral element of objects referenced by 'to' attributes. Provides a context for uniquifying the references in the 'to' attributes. Thus atoms referenced by ids should be unique within a given molecule and the id of this could be the 'toContext'. 2005-06-18: created</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="role"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The role of the link. Xlink adds semantics through a URI; we shall not be this strict. We shall not normally use this mechanism and use dictionaries instead.</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="href"> <xsd:annotation> <xsd:documentation> <h:div class="specific" xmlns:h="http://www.w3.org/1999/xhtml">The target of the (locator) link, outside the document.</h:div> </xsd:documentation> </xsd:annotation> </xsd:attributeGroup> <xsd:attributeGroup ref="linkType" /> </xsd:complexType> </xsd:element>

Definition Type:	Element
Name:	link
Namespace:	http://www.xml-cml.org/schema
Containing Schema:	schema.xsd
Abstract
Documentation:	An internal or external link to other objects. Semantics are similar to XLink, but simpler and only a subset is implemented. This is intended to make the instances easy to create and read, and software relatively easy to implement. The architecture is: A single element (link) used for all linking purposes. The link types are determined by the type attribute and can be:. locator. This points to a single target and must carry either a ref or href attribute. locator links are usually children of an extended link. arc. This is a 1:1 link with both ends (from and to) defined. extended. This is usually a parent of several locator links and serves to create a grouping of link ends (i.e. a list of references in documents). Many-many links can be built up from arcs linking extended elements All links can have optional role attributes. The semantics of this are not defined; you are encouraged to use a URI as described in the XLink specification. There are two address spaces: The href attribute on locators behaves in the same way as href in HTML and is of type xsd:anyURI. Its primary use is to use XPointer to reference elements outside the document. The ref attribute on locators and the from and to attributes on arcs refer to IDs (without the '#' syntax). Note: several other specific linking mechanisms are defined elsewhere in STM. relatedEntry should be used in dictionaries, and dictRef should be used to link to dictionaries. There are no required uses of link in STMML but we have used it to map atoms, electrons and bonds in reactions in CML Relation to XLink. At present (2002) we are not aware of generic XLink processors from which we would benefit, so the complete implementation brings little extra value. Among the simplifications from Xlink are: type supports only extended, locator and arc label is not supported and ids are used as targets of links. show and actuate are not supported. xlink:title is not supported (all STM elements can have a title attribute). xlink:role supports any string (i.e. does not have to be a namespaced resource). This mechanism can, of course, still be used and we shall promote it where STM benefits from it The to and from attributes point to IDs rather than labels The xlink namespace is not used It is not intended to create independent linkbases, although some collections of links may have this property and stand outside the documents they link to