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diff --git a/doc/xmldtd.html b/doc/xmldtd.html index 3f5a797..c5541d6 100644 --- a/doc/xmldtd.html +++ b/doc/xmldtd.html @@ -17,84 +17,84 @@ A:link, A:visited, A:active { text-decoration: underline } <li><a href="#Some">Some examples</a></li> <li><a href="#validate">How to validate</a></li> <li><a href="#Other">Other resources</a></li> -</ol><h3><a name="General5" id="General5">General overview</a></h3><p>Well what is validation and what is a DTD ?</p><p>DTD is the acronym for Document Type Definition. This is a -descriptionofthe content for a family of XML files. This is part of the -XML1.0specification, and allows one to describe and verify that a -givendocumentinstance conforms to the set of rules detailing its structure -andcontent.</p><p>Validation is the process of checking a document against a -DTD(moregenerally against a set of construction rules).</p><p>The validation process and building DTDs are the two most difficultpartsof -the XML life cycle. Briefly a DTD defines all the possible elementsto befound -within your document, what is the formal shape of your documenttree(by -defining the allowed content of an element; either text, aregularexpression -for the allowed list of children, or mixed content i.e.both textand -children). The DTD also defines the valid attributes for allelements andthe -types of those attributes.</p><h3><a name="definition1" id="definition1">The definition</a></h3><p>The <a href="http://www.w3.org/TR/REC-xml">W3C XML Recommendation</a>(<a href="http://www.xml.com/axml/axml.html">Tim Bray's annotated -versionofRev1</a>):</p><ul><li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaringelements</a></li> - <li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaringattributes</a></li> -</ul><p>(unfortunately) all this is inherited from the SGML world, the -syntaxisancient...</p><h3><a name="Simple1" id="Simple1">Simple rules</a></h3><p>Writing DTDs can be done in many ways. The rules to build them if -youneedsomething permanent or something which can evolve over time can -beradicallydifferent. Really complex DTDs like DocBook ones are flexible -butquiteharder to design. I will just focus on DTDs for a formats with a -fixedsimplestructure. It is just a set of basic rules, and definitely -notexhaustive norusable for complex DTD design.</p><h4><a name="reference1" id="reference1">How to reference a DTD from a document</a>:</h4><p>Assuming the top element of the document is <code>spec</code>and the -dtdisplaced in the file <code>mydtd</code>in the -subdirectory<code>dtds</code>ofthe directory from where the document were -loaded:</p><p><code><!DOCTYPE spec SYSTEM "dtds/mydtd"></code></p><p>Notes:</p><ul><li>The system string is actually an URI-Reference (as defined in <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>) so you can - useafull URL string indicating the location of your DTD on the Web. This - isareally good thing to do if you want others to validate - yourdocument.</li> - <li>It is also possible to associate a <code>PUBLIC</code>identifier(amagic - string) so that the DTD is looked up in catalogs on the clientsidewithout - having to locate it on the web.</li> - <li>A DTD contains a set of element and attribute declarations, - buttheydon't define what the root of the document should be. This - isexplicitlytold to the parser/validator as the first element - ofthe<code>DOCTYPE</code>declaration.</li> -</ul><h4><a name="Declaring2" id="Declaring2">Declaring elements</a>:</h4><p>The following declares an element <code>spec</code>:</p><p><code><!ELEMENT spec (front, body, back?)></code></p><p>It also expresses that the spec element contains one<code>front</code>,one -<code>body</code>and one optional<code>back</code>children elements inthis -order. The declaration of oneelement of the structure and its contentare done -in a single declaration.Similarly the following -declares<code>div1</code>elements:</p><p><code><!ELEMENT div1 (head, (p | list | note)*, div2?)></code></p><p>which means div1 contains one <code>head</code>then a series -ofoptional<code>p</code>, <code>list</code>s and <code>note</code>s and -thenanoptional <code>div2</code>. And last but not least an element -cancontaintext:</p><p><code><!ELEMENT b (#PCDATA)></code></p><p><code>b</code>contains text or being of mixed content (text and -elementsinno particular order):</p><p><code><!ELEMENT p (#PCDATA|a|ul|b|i|em)*></code></p><p><code>p </code>can contain text or -<code>a</code>,<code>ul</code>,<code>b</code>, <code>i </code>or -<code>em</code>elements inno particularorder.</p><h4><a name="Declaring1" id="Declaring1">Declaring attributes</a>:</h4><p>Again the attributes declaration includes their content definition:</p><p><code><!ATTLIST termdef name CDATA #IMPLIED></code></p><p>means that the element <code>termdef</code>can have -a<code>name</code>attribute containing text (<code>CDATA</code>) and which -isoptional(<code>#IMPLIED</code>). The attribute value can also be -definedwithin aset:</p><p><code><!ATTLIST list -type(bullets|ordered|glossary)"ordered"></code></p><p>means <code>list</code>element have a <code>type</code>attribute -with3allowed values "bullets", "ordered" or "glossary" and which -defaultto"ordered" if the attribute is not explicitly specified.</p><p>The content type of an attribute can be -text(<code>CDATA</code>),anchor/reference/references(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>),entity(ies)(<code>ENTITY</code>/<code>ENTITIES</code>) -orname(s)(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following -definesthat a<code>chapter</code>element can have an -optional<code>id</code>attributeof type <code>ID</code>, usable for reference -fromattribute of typeIDREF:</p><p><code><!ATTLIST chapter id ID #IMPLIED></code></p><p>The last value of an attribute definition can -be<code>#REQUIRED</code>meaning that the attribute has to be -given,<code>#IMPLIED</code>meaning that it is optional, or the default -value(possibly prefixed by<code>#FIXED</code>if it is the only allowed).</p><p>Notes:</p><ul><li>Usually the attributes pertaining to a given element are declared - inasingle expression, but it is just a convention adopted by a lot - ofDTDwriters: +</ol><h3><a name="General5" id="General5">General overview</a></h3><p>Well what is validation and what is a DTD ?</p><p>DTD is the acronym for Document Type Definition. This is a description of +the content for a family of XML files. This is part of the XML 1.0 +specification, and allows one to describe and verify that a given document +instance conforms to the set of rules detailing its structure and content.</p><p>Validation is the process of checking a document against a DTD (more +generally against a set of construction rules).</p><p>The validation process and building DTDs are the two most difficult parts +of the XML life cycle. Briefly a DTD defines all the possible elements to be +found within your document, what is the formal shape of your document tree +(by defining the allowed content of an element; either text, a regular +expression for the allowed list of children, or mixed content i.e. both text +and children). The DTD also defines the valid attributes for all elements and +the types of those attributes.</p><h3><a name="definition1" id="definition1">The definition</a></h3><p>The <a href="http://www.w3.org/TR/REC-xml">W3C XML Recommendation</a> (<a href="http://www.xml.com/axml/axml.html">Tim Bray's annotated version of +Rev1</a>):</p><ul><li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring + elements</a></li> + <li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring + attributes</a></li> +</ul><p>(unfortunately) all this is inherited from the SGML world, the syntax is +ancient...</p><h3><a name="Simple1" id="Simple1">Simple rules</a></h3><p>Writing DTDs can be done in many ways. The rules to build them if you need +something permanent or something which can evolve over time can be radically +different. Really complex DTDs like DocBook ones are flexible but quite +harder to design. I will just focus on DTDs for a formats with a fixed simple +structure. It is just a set of basic rules, and definitely not exhaustive nor +usable for complex DTD design.</p><h4><a name="reference1" id="reference1">How to reference a DTD from a document</a>:</h4><p>Assuming the top element of the document is <code>spec</code> and the dtd +is placed in the file <code>mydtd</code> in the subdirectory +<code>dtds</code> of the directory from where the document were loaded:</p><p><code><!DOCTYPE spec SYSTEM "dtds/mydtd"></code></p><p>Notes:</p><ul><li>The system string is actually an URI-Reference (as defined in <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>) so you can use a + full URL string indicating the location of your DTD on the Web. This is a + really good thing to do if you want others to validate your document.</li> + <li>It is also possible to associate a <code>PUBLIC</code> identifier (a + magic string) so that the DTD is looked up in catalogs on the client side + without having to locate it on the web.</li> + <li>A DTD contains a set of element and attribute declarations, but they + don't define what the root of the document should be. This is explicitly + told to the parser/validator as the first element of the + <code>DOCTYPE</code> declaration.</li> +</ul><h4><a name="Declaring2" id="Declaring2">Declaring elements</a>:</h4><p>The following declares an element <code>spec</code>:</p><p><code><!ELEMENT spec (front, body, back?)></code></p><p>It also expresses that the spec element contains one <code>front</code>, +one <code>body</code> and one optional <code>back</code> children elements in +this order. The declaration of one element of the structure and its content +are done in a single declaration. Similarly the following declares +<code>div1</code> elements:</p><p><code><!ELEMENT div1 (head, (p | list | note)*, div2?)></code></p><p>which means div1 contains one <code>head</code> then a series of optional +<code>p</code>, <code>list</code>s and <code>note</code>s and then an +optional <code>div2</code>. And last but not least an element can contain +text:</p><p><code><!ELEMENT b (#PCDATA)></code></p><p><code>b</code> contains text or being of mixed content (text and elements +in no particular order):</p><p><code><!ELEMENT p (#PCDATA|a|ul|b|i|em)*></code></p><p><code>p </code>can contain text or <code>a</code>, <code>ul</code>, +<code>b</code>, <code>i </code>or <code>em</code> elements in no particular +order.</p><h4><a name="Declaring1" id="Declaring1">Declaring attributes</a>:</h4><p>Again the attributes declaration includes their content definition:</p><p><code><!ATTLIST termdef name CDATA #IMPLIED></code></p><p>means that the element <code>termdef</code> can have a <code>name</code> +attribute containing text (<code>CDATA</code>) and which is optional +(<code>#IMPLIED</code>). The attribute value can also be defined within a +set:</p><p><code><!ATTLIST list type (bullets|ordered|glossary) +"ordered"></code></p><p>means <code>list</code> element have a <code>type</code> attribute with 3 +allowed values "bullets", "ordered" or "glossary" and which default to +"ordered" if the attribute is not explicitly specified.</p><p>The content type of an attribute can be text (<code>CDATA</code>), +anchor/reference/references +(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies) +(<code>ENTITY</code>/<code>ENTITIES</code>) or name(s) +(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a +<code>chapter</code> element can have an optional <code>id</code> attribute +of type <code>ID</code>, usable for reference from attribute of type +IDREF:</p><p><code><!ATTLIST chapter id ID #IMPLIED></code></p><p>The last value of an attribute definition can be <code>#REQUIRED +</code>meaning that the attribute has to be given, <code>#IMPLIED</code> +meaning that it is optional, or the default value (possibly prefixed by +<code>#FIXED</code> if it is the only allowed).</p><p>Notes:</p><ul><li>Usually the attributes pertaining to a given element are declared in a + single expression, but it is just a convention adopted by a lot of DTD + writers: <pre><!ATTLIST termdef id ID #REQUIRED name CDATA #IMPLIED></pre> - <p>The previous construct defines - both<code>id</code>and<code>name</code>attributes for the - element<code>termdef</code>.</p> + <p>The previous construct defines both <code>id</code> and + <code>name</code> attributes for the element <code>termdef</code>.</p> </li> -</ul><h3><a name="Some1" id="Some1">Some examples</a></h3><p>The directory <code>test/valid/dtds/</code>in the -libxml2distributioncontains some complex DTD examples. The example in -thefile<code>test/valid/dia.xml</code>shows an XML file where the simple -DTDisdirectly included within the document.</p><h3><a name="validate1" id="validate1">How to validate</a></h3><p>The simplest way is to use the xmllint program included with -libxml.The<code>--valid</code>option turns-on validation of the files given -asinput.For example the following validates a copy of the first revision of -theXML1.0 specification:</p><p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p><p>the -- noout is used to disable output of the resulting tree.</p><p>The <code>--dtdvalid dtd</code>allows validation of the -document(s)againsta given DTD.</p><p>Libxml2 exports an API to handle DTDs and validation, check the <a href="http://xmlsoft.org/html/libxml-valid.html">associateddescription</a>.</p><h3><a name="Other1" id="Other1">Other resources</a></h3><p>DTDs are as old as SGML. So there may be a number of examples -on-line,Iwill just list one for now, others pointers welcome:</p><ul><li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li> -</ul><p>I suggest looking at the examples found under test/valid/dtd and any -ofthelarge number of books available on XML. The dia example in -test/validshouldbe both simple and complete enough to allow you to build your -own.</p><p></p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html> +</ul><h3><a name="Some1" id="Some1">Some examples</a></h3><p>The directory <code>test/valid/dtds/</code> in the libxml2 distribution +contains some complex DTD examples. The example in the file +<code>test/valid/dia.xml</code> shows an XML file where the simple DTD is +directly included within the document.</p><h3><a name="validate1" id="validate1">How to validate</a></h3><p>The simplest way is to use the xmllint program included with libxml. The +<code>--valid</code> option turns-on validation of the files given as input. +For example the following validates a copy of the first revision of the XML +1.0 specification:</p><p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p><p>the -- noout is used to disable output of the resulting tree.</p><p>The <code>--dtdvalid dtd</code> allows validation of the document(s) +against a given DTD.</p><p>Libxml2 exports an API to handle DTDs and validation, check the <a href="http://xmlsoft.org/html/libxml-valid.html">associated +description</a>.</p><h3><a name="Other1" id="Other1">Other resources</a></h3><p>DTDs are as old as SGML. So there may be a number of examples on-line, I +will just list one for now, others pointers welcome:</p><ul><li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li> +</ul><p>I suggest looking at the examples found under test/valid/dtd and any of +the large number of books available on XML. The dia example in test/valid +should be both simple and complete enough to allow you to build your own.</p><p></p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html> |