XML Validation I DTDs Robin Burke ECT 360 Winter 2004

Outline History Grammars / Regular expressions DTDs elements attributes entities Declarations

Validation Why bother?

The idea Language consists of terminals a, b, c Set of productions beginning with non-terminals A, B, C rules specifying how to generate sequences of terminals

Example A  aB A  aBA B  b generates strings ababab etc.

Grammar Can be used to efficiently parse a language basis of all modern programming language parsing since Algol-60 Java Language Specification is completely in EBNF grammar

Grammar XML grammar-based syntax adheres to EBNF SGML SGML had a more complex language definition syntax HTML is defined the SGML way

Regular expressions Language for expressing patterns Basic components pattern elements optional element = ? repetition (1 or more) = + repetition (0 or more) = * choice = | grouping = ( ) sequence =,

Examples (a, b)* all strings "ab" "abab" etc. (a | b | c)+, q, (b, c)* aaqb bq bqcccccccc

Note Regular expressions are different in different applications Perl Javascript XML Schemas DTDs only support ?+*|,()

EBNF EBNF is more compact version of BNF it uses regular expressions to simplify grammar expression A  aB A  aBA turns into A  aB(A)? only one production per non-terminal allowed

DTDs Use EBNF to specify structure of XML documents Plus attributes entities Syntax holdover from SGML Ugly

DTD Syntax Content model contains the RHS of the production rule Example <!ELEMENT name (firstName, lastName)>

DTD Syntax cont'd Not XML <! begins a declaration No "content" Empty elements not indicated with />

Simple content models Content can be any text #PCDATA Content can be anything at all (useful for debugging) ANY Element has no content EMPTY

Example Jane Doe A John Doe A-

Example Jane Doe A John Doe A- Wayne Doe I Alien abduction

DTD?

Mixed content Legal to have a content model with text and element data President Meets with Congress The President meet with Congressional leaders today in effort to jump-start faltering budget negotiations. Sources described the mood of the meeting as "cordial".

Mixed content, cont'd Mixed content makes handling XML complex necessary for many applications

Recursion Unlike grammars recursive formulation ≠ repetition Difference between

Restriction The grammar cannot be ambiguous A  (a, b)| (a, c) this makes the parser implementation difficult Usually easy to make non-ambiguous A  a, (b | c)

Attribute lists Declared separately from elements can be anywhere in the DTD Specification includes name of the element name of the attribute attribute type default

Attribute types Character data CDATA different from XML CDATA section! Enumerated (yes|no) ID must be unique in the document IDREF must refer to an id in the document NMTOKEN a restriction of CDATA to single "word" Also IDREFS and NMTOKENS

Default declaration #REQUIRED #IMPLIED means optional Value this becomes the default #FIXED value provided

Examples <!ATTLIST img src CDATA #REQUIRED alt CDATA #REQUIRED align (left|right|center) "left" id ID #IMPLIED > <!ATTLIST timestamp time-zone NMTOKEN #IMPLIED>

Entities Like macros content to be inserted indicated with &name; Predefined general entities & < essential part of XML User-defined general entities &disclaimer;

Entities, cont'd Parameter entities can also be used to simplify DTD creation or to combine DTDs indicated with a % More on this next week

Defining general entities Example <!ENTITY disclaimer "This is a work of fiction. Any resemblance to persons living or dead is unintentional.">

In-class exercise Business cards

Next week More DTDs Entities Modularization and parameterization pg

Lab