XML Schema

1
XML Schema

• http//www.w3c.org/XML/Schema

2
XML Schema

• A definition language that enables you to
  constrain conforming XML documents to a specific
  vocabulary and a specific hierarchical structure
• Element types, attribute types, complex types
• Two types of documents a schema document and
  multiple instance documents that conform to the
  schema
• A schema definition is a blueprint (template) of
  a type and each instance is an incarnation of
  that template
• Two roles that a schema can play
• Template for a form generator to generate
  instances of a document type
• Validator to ensure the accuracy of documents

3
Schema and Instances
4
XML Schema (Cont.)

• Both the schema document and the instance
  document use XML syntax (tags, elements, and
  attributes)
• Each instance document must declare which schema
  it adhere to
• Use a special attribute attached to the root
  element called"xsinoNamespaceSchemaLocation"
  or"xsischemaLocation"
• Depend on whether your vocabulary is defined in
  the context of a namespace
• XML Schemas allow validation of instances to
  ensure the accuracy of field values and document
  structure at the time of creation
• Field types, legal element and attribute names,
  correct number of children, and required
  attributes

5
What do Schemas Look Like?

• An XML Schema uses XML syntax to declare a set of
  simple and complex type declarations
• A type is named template that can hold one or
  more values
• Simple types hold one value
• Complex types are composed of multiple simple
  types
• A type has two key characteristics a name and a
  legal set of values
• Simple type an element declaration that includes
  its name and value constraints
• ltxsdelement name"author" type"xsdstring" /gt
• ltauthorgt Mike Daconta lt/authorgt

6
Common XML Schema Primitive Data Types
You can define custom data types
7
Define Custom Data Types
ltxsdsimpleType name"skuType"gt
ltxsdrestriction base"xsdstring"gt
ltxsdpattern value"\d 3 -A-Z 2 "/gt
lt/xsdrestrictiongt lt/xsdsimpleTypegt
ltxsdsimpleType name"stateType"gt
ltxsdrestriction base"xsdstring"gt
ltxsdenumeration value"AK"/gt
ltxsdenumeration value"AL"/gt
ltxsdenumeration value"AR"/gt ...
lt/xsdrestrictiongt lt/xsdsimpleTypegt

ltxsdsimpleType name"poIdType"gt
ltxsdrestriction base"xsdinteger"gt
ltxsdminExclusive value"10000"/gt
ltxsdmaxExclusive value"100000"/gt
lt/xsdrestrictiongt lt/xsdsimpleTypegt
8
What do Schemas Look Like? (Cont.)

• Complex type an element that either contains
  other elements or has attached attributes
• ltxsdelement name"book" ltxsdcomplexTypegt
  ltxsdattribute name"title" type"xsdstring" /gt
  ltxsdattribute name"pages" type"xsdint" /gt
  lt/xsdcomplexTypegtlt/xsdelementgt
• ltbook title"More Java Pitfalls" page"453" /gt

9
What do Schemas Look Like? (Cont.)

• Another example of Complex type
• ltxsdelement name"product" ltxsdcomplexTypegt
  ltxsdsequencegt ltxsdelement
  name"description" type"xsdstring"
  minOccurs"0" maxOccurs"1" /gt ltxsdelement
  name"category" type"xsdstring"
  minOccurs"1" maxOccurs"unbounded" /gt lt/xsd
  sequencegt ltxsdattribute name"id"
  type"xsdID" /gt ltxsdattribute name"title"
  type"xsdstring" /gt ltxsdattribute
  name"price" type"xsddecimal" /gt
  lt/xsdcomplexTypegtlt/xsdelementgt

10
What do Schemas Look Like? (Cont.)

• ltproduct id"P01" title"Wonder Teddy"
  price"49.99"gt ltdescriptiongt The best selling
  teddy bear of the year. lt/descriptiongt
  ltcategorygt toys lt/categorygt ltcategorygt stuffed
  animals lt/categorygtlt/productgt
• ltproduct id"P02" title"RC Racer"
  price"89.99"gt ltcategorygt toys lt/categorygt
  ltcategorygt electronic lt/categorygt ltcategorygt
  radio-controlled lt/categorygt
• lt/productgt

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What do Schemas Look Like? (Cont.)

• Let's Look at a more complex Schema po.xsd

12
Purchase Order Schema
13
Reusability

• Basic reusability mechanisms address the problems
  of using existing assets in multiple places.
• Element references
• Content model groups
• Attribute groups
• Schema includes
• Schema imports
• Advanced reusability mechanisms address the
  problems of modifying existing assets to serve
  needs that are perhaps different from what they
  were originally designed for
• Exploit object-oriented idea
• Extension and Restrictions

14
Is Validation Worth the Trouble?

• Validation, and the tool support for it, is still
  evolving
• Until the schema languages mature, validation
  will be a frustrating process that requires
  testing with multiple tools
• Validation is a critical component of your data
  management process, because
• XML is intended to be shared and processed by a
  large number and variety of applications
• A source document may be broken up into XML
  fragments and parts reused ? the cost of errors
  in XML must be multiplied across all the programs
  and partners that rely on that data
• The chief difficulties with validation data
  types, namespace support, and type inheritance