Unit 4 – XML Schema XML - Level I Basic

Unit objectives  Identify the limitations of DTDs  Describe schema and its components  Create and modify schema Unit 4 - Schema 7/14/2013 Copyright © Carl M. Burnett 2

Topic A  Topic A: XML Schema  Topic B: Schema description and components  Topic C: Creating a schema 7/14/2013 Copyright © Carl M. Burnett 3

XML Schema  Document type definitions (DTDs) provide a mechanism for modeling XML languages  Developed to overcome the limitations of DTDs 7/14/2013 Copyright © Carl M. Burnett 4

Disadvantages of DTDs  Special syntax  Can not be processed by a standard XML processor  Limited ability to describe the data in elements and attributes  Limited support for namespaces  New names required for similar elements in different contexts of the same document 7/14/2013 Copyright © Carl M. Burnett 5

XML Schema recommendations Schema  An application of XML  Defines a model for describing the structure and content of data  Referred to as XML Schema or XSchema  Facilitates development of better data descriptions and definitions of shared markup vocabularies 7/14/2013 Copyright © Carl M. Burnett 6

Topic B  Topic A: XML Schema  Topic B: Schema description and components  Topic C: Creating a schema 7/14/2013 Copyright © Carl M. Burnett 7

Schema model  Constraint defines what can appear in a given language or document  Content model constraint  Defines the elements that can appear  Datatype constraint  Describes the units of data that the schema considers valid  Class of documents - individual schemas  Instance documents - XML documents that conform to a particular schema 7/14/2013 Copyright © Carl M. Burnett 8

Schema components  The prolog  First 3 lines of the schema  First line is the XML declaration ( ) - mandatory  Next 2 lines are comment lines ( ) 7/14/2013 Copyright © Carl M. Burnett 9

Schema element  Namespace in schema  schema element  Conforms to W3C Schema recommendation  Namespace declaration  xmlns:xs=  “xmlns” - namespace declaration  “xs” - abbreviation to relate the respective elements or datatypes to the namespace  - the unique Uniform Resource Identifier (URI) continued 7/14/2013 Copyright © Carl M. Burnett 10

Schema element, continued  Qualified and unqualified locals  Local elements are declared in subelements of the schema element, but not in the scope of schema  Global declared elements are declared in the element  Prefixed element names are qualified names  Element names without prefixes are unqualified names 7/14/2013 Copyright © Carl M. Burnett 11

XML schema document validation 7/14/2013 Copyright © Carl M. Burnett 12

Qualified locals 7/14/2013 Copyright © Carl M. Burnett 13

Unqualified locals 7/14/2013 Copyright © Carl M. Burnett 14

Element types and compositors  Complex type  Determines appearance and content in XML-related instance documents  Contains attributes and/or subelements  Simple type  Contains no attributes or subelements, just character data  Compositors  Define groups of element and attributes  Might be nested inside of one another 7/14/2013 Copyright © Carl M. Burnett 15

Types of compositors  Sequence compositor  Elements must appear in the same order as indicated in the schema  Choice compositor  Allows only one element to appear in the XML document at that point  All compositor  Allows any of the elements to appear in any order 7/14/2013 Copyright © Carl M. Burnett 16

Attributes and cardinality  The number of times an element may occur in instance document  Denoted by a plus sign (+) that indicates it must occur at least once  No limit to the number of times it might occur  XML Spy substituted attributes:  minOccur and maxOccur (minimum and maximum number of occurrences) 7/14/2013 Copyright © Carl M. Burnett 17

Subelements  Simple types of elements  Defined in the W3C Schema Recommendation (XML Schema)  Use prefix xs:  Defined by the schema designer according to specific needs  Russian Doll or nesting approach - A full element declaration is inserted every time the element is needed  Flat catalog approach – employs global references 7/14/2013 Copyright © Carl M. Burnett 18

Simple types 7/14/2013 Copyright © Carl M. Burnett 19

Other schema facets 7/14/2013 Copyright © Carl M. Burnett 20

Topic C  Topic A: XML Schema  Topic B: Schema description and components  Topic C: Creating a schema 7/14/2013 Copyright © Carl M. Burnett 21

Creating schemas  You can use XML Spy to create schemas  You can use XML Spy to convert an existing DTD to a schema 7/14/2013 Copyright © Carl M. Burnett 22

Student Exercises  Topic C – Creating a Schema  C-1: Converting a DTD to Schema  C-2: Creating XML Schema from scratch  C-3: Adding Global Components in a Schema 7/14/ Copyright © Carl M. Burnett

Unit summary  Identify the limitations of DTDs  Described schema and its components  Learned how to create and modify schema 7/14/2013 Copyright © Carl M. Burnett 24