XML Data (schema)
XML-Data
W3C Note January 5, 1998
- XML-Data was the first in a series of papers to describe a method for creating XML data schema.
- An XML data schema allows you to define constraints on the structure of an XML document.
Presentation Outline
• Why do we need XML Data Schema? (Isn’t a DTD good enough?)
• How XML Data Schemas are Used
• Features of XML Data Schema
• Summary
Why do we need XML Data Schema?
Schema Definition in SQL:
create table account
(account-number char(10) not null,
branch-name char(15),
balance integer,
primary key (account-number),
foreign key (branch-name) references branch,
check (balance >=0))
A DTD that is not quite equivalent to the above schema
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Why do we need XML Data Schema?
“Equivalent” XML Data Schema
Features of XML Data Schema
Many primitive datatypes are available and new datatypes can be defined
John Doe
123 Maple Street
Ann Arbor
MI
48109
Features of XML Data Schema
Attribute group definitions provide a construct to replace some uses of parameter entities.
...
Features of XML Data Schema
New element types can be defined by adding additional content to the content model of another type definition
John
Doe
Doe
Jr
Features of XML Data Schema
New element types can be defined by adding restrictions or eliminating content from another type definition
John
Doe
Features of XML Data Schema
Using “unique” and “key” constraints, the capabilities of XML’s ID/IDREF mechanism have been extended
Element content and combinations of attribute values and content can be declared to be unique
Combinations of attribute values and/or element content can be declared to be keys (not only unique, but always present)
Constraints can have document-wide scope or hold within the scope of particular elements
Features of XML Data Schema
. . .
. . .
.//vehicle[@regNo]
@regNo
ancestor::state/stateCode
How XML Data Schema are Used
Sample XML Data Schema
How XML Data Schema are Used
Sample XML Document that Conforms to the Schema
John Doe
50
Jane Doe
50
How XML Data Schema are Used
An XML data schema is expressed in XML instance syntax
An XML data schema must be valid with respect to a schema DTD
An XML document can identify a schema to which it is supposed to conform
An XML document is schema-valid with respect to a schema if it meets the structural and datatyping constraints expressed in the schema
The XML document processor must be schema-aware to determine if a document is schema-valid
Summary
XML Data Schemas provide a powerful mechanism for defining datatypes and constraints on document structure
XML Data Schemas are expressed in XML instance syntax
The XML document processor must be schema-aware to determine if a document is valid with respect to a schema
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