XML Schema Part 0: Primer Second Edition - 1 views
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The schemaLocation attribute value consists of one or more pairs of URI references, separated by white space. The first member of each pair is a namespace name, and the second member of the pair is a hint describing where to find an appropriate schema document for that namespace
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there is a noNamespaceSchemaLocation attribute which is used to provide hints for the locations of schema documents that do not have target namespaces.
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the include element has a required schemaLocation attribute, and it contains a URI reference which must identify a schema document.
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the import element has optional namespace and schemaLocation attributes. If present, the schemaLocation attribute is understood in a way which parallels the interpretation of xsi:schemaLocation
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The default value for both the minOccurs and the maxOccurs attributes is 1.
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Be sure that if you specify a value for only the minOccurs attribute, it is less than or equal to the default value of maxOccurs,
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Attributes may appear once or not at all, but no other number of times
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The existence of a substitution group does not require any of the elements in that class to be used
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Several facets can be applied to list types: length, minLength, maxLength, pattern, and enumeration
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<xsd:simpleType name="USStateList"> <xsd:list itemType="USState"/> </xsd:simpleType> <xsd:simpleType name="SixUSStates"> <xsd:restriction base="USStateList"> <xsd:length value="6"/> </xsd:restriction> </xsd:simpleType>
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USState es una enumeración, definida en este documento en la sección 2.3. ASí, precisamos siempre de un tipo de dato definido previamente para construir una lista.
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Note that it is possible to derive a list type from the atomic type string. However, a string may contain white space, and white space delimits the items in a list type, so you should be careful using list types whose base type is string.
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The include mechanism enables you to use externally created schema components "as-is", that is, without any modification.
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<complexType name="Address">
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base="ipo:Address"
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El tipo base y el extendido tienen igual identificador.
Fuera del elemento "redefine" cualquier intento de nombrar a dos tipos de datos usando el mismo identificador producirá un error.
Notar cómo el elemento "redefine" debe ser el primer hijo del elemento "schema" y encerrar al tipo de dato que redefinimos.
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</redefine>
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The redefine element acts very much like the include element as it includes all the declarations and definitions from the address.xsd file
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Outside of the redefine element, any such attempt to define a complex type with the same name (and in the same namespace) as the base from which it is being derived would cause an error.
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Now that Address has been redefined, the extension applies to all schema components that make use of Address
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Cuando un elemento es redefinido, la extensión se aplica a todos los tipos de datos que hacen uso de él como, p.e., sus tipos derivados (ver sección 4.2 y 4.3, así como los ejemplos en Creaweb).
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Substitution GroupsXML Schema provides a mechanism, called substitution groups, that allows elements to be substituted for other elements. More specifically, elements can be assigned to a special group of elements that are said to be substitutable for a particular named element called the head element. (Note that the head element as well as the substitutable elementsmust be declared as global elements
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Elements in a substitution group must have the same type as the head element, or they can have a type that has been derived from the head element's type
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<element name="shipComment" type="string" substitutionGroup="ipo:comment"/>
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substitutionGroup="ipo:comment"/>
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<ipo:shipComment>
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- no todos los elementos del grupo de sustitución han de aparecer en la instancia XML. - los indicadores minOccurs y maxOccurs del elemento cabecera deben ser adecuados al número de elementos de sustitución que permitamos aparecer (pueden aparecer tantos como el valor maxOccurs del elemento cabecera). - si maxOccurs así lo permite, puede aparecer el elemento cabecera y sus sustitutos.
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<ipo:customerComment>
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global declarations cannot contain the attributes > minOccurs > , > maxOccurs > , or > use > . >
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Abstract Elements and TypesXML Schema provides a mechanism to force substitution for a particular element or type. When an element or type is declared to be "abstract", it cannot be used in an instance document. When an element is declared to be abstract, a member of that element's substitution group must appear in the instance document. When an element's corresponding type definition is declared as abstract, all instances of that element must use xsi:type to indicate a derived type that is not abstract.
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Declaring an element as abstract requires the use of a substitution group. Declaring a type as abstract simply requires the use of a type derived from it (and identified by the xsi:type attribute) in the instance document
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the redefine mechanism we describe here enables you to redefine simple and complex types, groups, and attribute groups that are obtained from external schema files. Like the include mechanism, redefine requires the external components to be in the same target namespace as the redefining schema,
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abstract="true"
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abstract="true"
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extension base
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extension
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extension
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xsi:type="Car"
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Controlling the Creation & Use of Derived Types
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schema authors will sometimes want to control derivations of particular types, and the use of derived types in instances.
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to specify that for a particular complex type, new types may not be derived from it, either (a) by restriction, (b) by extension, or (c) at all.
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substitutionGroup=
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The restriction value of the final attribute prevents derivations by restriction. Preventing derivations at all, or by extension, are indicated by the values #all and extension respectively
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an optional finalDefault attribute on the schema element whose value can be one of the values allowed for the final attribute. The effect of specifying the finalDefault attribute is equivalent to specifying a final attribute on every type definition and element declaration in the schema.
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When a simple type is defined, the fixed attribute may be applied to any of its facets to prevent a derivation of that type from modifying the value of the fixed facets.
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fixed="true"
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a mechanism that controls which derivations and substitution groups may be used in instance documents
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eplacement by derived types can be controlled using the block attribute in a type definition
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Previene la sustitución de un elemento por su tipo derivado, bien sea por extensión o restricción. No confundir este mecanismo con "final", que sólo previene la definición de tipos derivados (por extensión o restricción) de un tipo determinado.
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final="restriction"
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final="restriction"
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Preventing replacement by derivations at all, or by derivations-by-extension, are indicated by the values #all and extension respectively. As with final, there exists an optional blockDefault attribute on the schema element whose value can be one of the values allowed for the block attribute.
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block="restriction"
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final="restriction"
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mechanism that enables schema components from different target namespaces to be used together, and hence enables the schema validation of instance content defined across multiple namespaces.
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Importing Types
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only global schema components can be imported:
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Only named complex types can be imported; local, anonymously defined types cannot.
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each namespace must be identified with a separate import element.
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The import elements themselves must appear as the first children of the schema element
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each namespace must be associated with a prefix, using a standard namespace declaration
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import elements optionally contain a schemaLocation attribute to help locate resources associated with the namespaces.
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ref="xipo:
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Deriving Types by Extension
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we indicate that the content models of the new types are complex, i.e. contain elements, by using the complexContent element, and we indicate that we are extending the base type Address by the value of the base attribute on the extension element.
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xsi:type="ipo:UKAddress">
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xsi:type="ipo:USAddress">
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Deriving Complex Types by Restriction
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the values represented by the new type are a subset of the values represented by the base type (as is the case with restriction of simple types).
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<complexContent> <restriction base=
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Table 3 shows several examples of how element and attribute declarations within type definitions may be restricted
