XML Schemas J. Pontes November 15, 2004

Schemas  Defines what a set of one or more document can look like.  What elements it contains, order, content, and attributes.  These documents are written in XML Schema language

DTD Disadvantages compared to XML  Cannot be parsed by an XML parser  All declarations in DTD are global (impossible to define two elements with same name.)  DTD cannot control what kind of information a given element or attribute can contain.

What XML Schema Buys You  One can define both global elements (used same way all along document) and local elements (particular meaning in a particular context).  XML Schemas contain a system of data types.  Gives more control over XML document

Schema: types of content  Simple Type – text only  Complex Types – contain other elements or attributes.

Simple Type  Date  Integer  String  Customer built types –In DTD we used #OCDATA to capture a name, a date or practically anything.

Complex Type  Describe the structure of a document, rather than content.  Complex Types –Elements that contain elements –Elements that contain element and text –Elements that contain only text –Elements that are empty Each may contain attributes

Examples of Built-in Simple Types

Custom Simple Type This type limits the content of elements (zipcodeType) to a string with 5 digits, an optional hyphen and 4 extra digits.

Complex Type Definition <xsd:element name=“animal” type=“animalType” minOccurs=“1” maxOccurs=“unbounded”/> Defines endType. It contains another element animal defined with another complex type animalType to define a particular element

Local end Global declarations  Global –Declared at top level of a schema, just immediately below xsd:schema element. They are available to be used throughout the the rest of the schema. –Global element declaration do not determine where an element can appear in the XML document – they only determine what the element will look like. –A global element declaration must be explicitly referenced in order to have it appear in a corresponding XML document.  Simple –Locally declared elements. Limited to the complex type definition in which they are declared and may not not be used elsewhere in the schema. –Such locally declared elements are automatically referenced.

Example of Local and Global Elements <xsd:element ref=“name” minOccurs=“2”/> … automatically referenced. manually referenced. Same name different definitions.

Cont’d <xsd:element ref=“name” minOccurs=“1” maxOccurs=“unbounded”/> … … Same name different definitions.

Beginning a Simple Schema //Declaring XML <xsd:schema xmlns:xsd=“ ”  Any element or type that is prefixed with xsd: will be recognized as coming from namespace*  Schema rules go in this space.  Save you schema as a text only with the.xsd extension.

Indicating a Location <endanged_species xmlns:xsd=“ ” xsi:noNamespaceSchemaLocation= “ ”> * * file.xsd previously created.

Making Schemas Annotations <xsd:schema xmlns:xsd=“ ” This schema will be used to validate the set of XML documents for the Endangered Species Project.

Defining Simple Types  When declaring an element, you choose its name and what kind of content it should contain. –xsd:string – string of characters –xsd:decimal – decimal number –xsd:boolean – true of false –xsd:date – CCYY-MM-DD –xsd:time - –xsd:uriReference - element will contain an URL –xsd:language – two letter language listed in ISO639 –Custom – name of a custom simple type. –Code.xsd –Code.xml 500 pounds 28 When a value is an integer or a string?

More XML Data Types  Click Here for More Data Types Click Here for More Data Types

Date and Time Data Types  Code.xsd <xsd:element name=“gestation” type=“xsd:timeDuration”/> (represent a certain amount of time)  Code.xml P3M15D (PnYnMnDTnHnMnS) Period n - non negative T begins optional time section

 Code.xsd xsd:element name=“bedtime” type=“xsd.time:/>  Code.xml 20:15:05-05:00>/bedtime> Date and Type Data Types

Additional xsd:time  xsd:time (hh:mm:ss.sss)  xsd:timeInstant (CCYY-MM-DDTh:mm:ss.sss)  xsd:date CCYY-MM-DD  xsd:month (CCYY-MM  xsd:year (CCYY)  xsd:century (CC)  xsd:recurringDate  xsd:recurringDay

Number Type  xsd:decimal  xsd:integer  xsd:positiveinteger  xsd:negativeinteger  xsd:float  xsd:double

XML Validator  STG XML Validation