- XML. - DTDs - XML Schema - XSLT. Web Services. - Well-formedness is a REQUIRED check on XML documents

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Ophelia Williamson
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1 Purpose of this day Introduction to XML for parliamentary documents (and all other kinds of documents, actually) Prof. Fabio Vitali University of Bologna Introduce the principal aspects of electronic management of documents - What we actually mean by documents (the FRBR hierarchy) - What are the components of documents - What do we mean by data and metadata about documents Introduce some technologies related to electronic management of documents - XML - DTDs - XML Schema - XSLT - RDF and OWL all somehow connected and related to parliamentary documents (but not necessarily only to them) Part 2 Next: An overall view 2/33 SGML HTML XHTML CSS XSLT An overall view XML browser NS XPath XPointer XLink URI XML Schema DOM XSLFO SOAP Java, C, C++, PHP, ASP, Perl, Javascript, VBscript Web Services print Well-formedness and validity They are two different types of correctness in XML language: Well-formedness - This is the basic level, whereby all syntactic and nesting rules are followed but no constraints on vocabulary or containment is checked. - Well-formedness requires no DTD to be assessed, but just an evaluation of the document in and by itself. - Well-formedness is a REQUIRED check on XML documents Validation - Validation is the subsequent level, whereby also constraints on vocabulary and containment are checked - Validation requires a DTD (or an XML schema) - Validation is an OPTIONAL check on XML documents. Next: Well-formedness and validity 3/33 Next: Well-formed XML documents 4/33 Well-formed XML documents An XML document is well-formed if: - All start and end tag match and are correctly nested - A global element exists to contain all the others - Empty elements have a bar at the end of the element: <empty/> - All attributes always use matching quotes or doublequotes: <element att="value"> </element> <element att='value'> </element> - All character entities are explicitly defined A single example of all bad formedness types <article id=art01> <num>1.</num> <title>definitions and application</title> <clause id='art01-cla01"> nothing contained in this Act may be <eol>construed as correct XML. <article id= art02 > <num>2.</num> <title>recognition of incorrect XML</title> <clause id="art02"cla01"> a text may not be in bold, then in bold and italic and then only italic. Next: A single example of all bad formedness types 5/33 Next: and the corresponding well- formed XML fragment 6/33 1

2 and the corresponding wellformed XML fragment <akomantoso> <article id="art01"> <num>1.</num> <title>definitions and application</title> <clause id='art01-cla01'> nothing contained in this Act may be <eol/ >construed as correct XML. <article id="art02"> <num>2.</num> <title>recognition of incorrect XML</title> <clause id='art02"cla01'> a text may not be in bold, then in bold and italic and then only italic. </akomantoso> XML documents An XML document is always composed of three parts: - XML Declaration - Document Type Declaration (or DOCTYPE) - The document instance Next: XML documents 7/33 Next: A complete XML example 8/33 A complete XML example <?xml version="1.0" encoding="utf-8"?> <!DOCTYPE akomantoso SYSTEM " <akomantoso xmlns=" <article id="art01"> <num>1.</num> <title>definitions and application</title> <clause id='art01-cla01'> nothing contained in this Act may be construed as correct XML. <article id="art02"> <num>2.</num> <title>recognition of incorrect XML</title> <clause id='art02"cla01'> a text may not be in bold, then in bold and italic and then only italic. </akomantoso> Next: XML Declaration 9/33 XML Declaration <?xml version="1.0" encoding="utf-8" standalone="no"?> The XML declaration is (virtually) required and contains all optional features of XML, that are exactly three: - The XML language version (1.0 or 1.1 but 1.1 is not really used anywhere much) - The character encoding used (we will mostly use UTF-8) - The standalone parameter, used for efficiency purposes If omitted, it need to be considered equivalent to: <?xml version="1.0"?> Next: The Document Type Declaration (or DOCTYPE) 10/33 The Document Type Declaration (or DOCTYPE) <!DOCTYPE akomantoso SYSTEM " The document type declaration specifies the location or contains the validation constraints of the document These validation constraints are called Document Type Definition (or DTD) and are either: - Contained in a file referred to by the DOCTYPE (external subset) - Contained in the DOCTYPE itself (internal subset) - Partly internal and partly external <!DOCTYPE akomantoso [ ELEMENT akomantoso (bill act debaterecord document)>... ]> The document instance The part of document that contains text and markup. Markup is considered composed of elements and attributes. The document instance is checked against the constraints specified in the DTD, if present. This is the validation of the document instance. Next: The document instance 11/33 Next: DTDs 12/33 2

3 Element specification: <!ELEMENT > DTDs <!ELEMENT >: Element definitions <!ATTLIST >: Attribute definitions <!ENTITY % >: Parameter entities <!ELEMENT name content-model > <!ELEMENT act (meta,preface?,preamble?,clauses,attachments?) > The ELEMENT clauses introduces a single element. It specifies the name and the content model of the element. All elements of the specification must be introduced explicitly (but in any order) The content model is the formal specification of the allowed content of the element, in terms of what other elements can appear. The content model can be "ANY", "EMPTY", or a parenthesised expression containing #PCDATA and other XML elements aggregated with simple operators. - Repetition operators (nothing, question mark, plus, star) - Sequence operator (comma, pipe) Next: Content models (1) 14/33 ANY Content models (1) - Any content is allowed. Very general, it is only used when standardisation is impossible. We will not further use it EMPTY - Empty elements appear as simple tags with special ending slash <empty/>. The element is completely constituted by its start tag. It can have attributes, though. <img src="image.gif"/> (#PCDATA) - A (#PCDATA) element only contains text, and no markup whatsoever. Used when using XML to wrap plain text elements. <!ELEMENT title (#PCDATA)> Content model (2) - Operators Repetition Operators: applied at the end of individual elements or parenthesised expressions, they indicate how that token can repeat - Nothing: token is required and non-repeatable: one and only one can be present - Question mark: token is optional and non-repeatable: zero or one can be present - Plus: token is required and repeatable: one or more can be present - Star: token is optional and repeatable: zero, one or more can be present. Sequence Operators: applied in between individual elements or parenthesised expressions, they indicate how these tokens can interact: - Comma: the tokens are in sequence. Tokens need to appear exactly in the order specified - Pipe: the tokens are alternative. Only one token can appear to the exclusion of the other(s). Next: Content model (2) - Operators 15/33 Next: Content models (3) - examples 16/33 Content models (3) - examples <!ELEMENT akomantoso (act bill debaterecord) > <!ELEMENT part (num?, title?, section+) > <!ELEMENT dummy ((first (second, third)*), fourth?)> Parliamentary-relevant content models are hardly ever this complex. Please note that a repeatable alternative (a b k)+ has a very specific interpretation: any specified token can appear any number of times in any order whatsoever. <!ELEMENT part (num?, title?, (part section article)+) > (a+ b+ c+) NOT EQUAL TO (a b c)+ Examples <!ELEMENT dummy ((first (second, third)*), fourth?)> <dummy> <first> </first> <fourth> </fourth> </dummy> <dummy> <second> </second> <third> </third> <second> </second> <third> </third> <fourth> </fourth> </dummy> Next: Examples 17/33 Next: Content models (4) - Mixed content 18/33 3

4 Content models (4) - Mixed content <!ELEMENT p (#PCDATA b i )* > It is sometimes appropriate that an element contain both printable characters and other elements. These elements are defined as having "mixed content". a text may be in bold, or in bold and italic. Or even only in italic. XML DTDs only allow one form of Mixed Content elements: - An optional repeatable alternative (... )* - containing all the allowed elements (... a b c)* - of which #PCDATA must be the first. (#PCDATA a b c)* Attribute specification: <!ATTLIST > <!ATTLIST element-name attribute-name-1 type-1 default-1 attribute-name-2 type-2 default-2 attribute-name-3 type-3 default-3 > <!ATTLIST act contains (Original Single Multiple) 'Original' > <act contains="single">... </act> The ATTLIST clause introduce the definition of a list of attributes for an element. The number of attributes that can be defined for the same element is open. There are four kinds of types and three kinds of defaults Next: Attribute specification: <!ATTLIST > 19/33 Next: Attribute specification: types and defaults 20/33 Attribute specification: types and defaults Attribute specification: examples Types - CDATA: any character string - List: a choice of only the character string listed - ID: a single word that is unique throughout the document - IDREF: a word that is used somewhere in the document as the value for an ID attribute Defaults - A (quoted) explicit value: the specified value - #REQUIRED: no default value, but the attribute is required for validity - #IMPLIED: no default value, and the attribute is not required for validity <!ATTLIST section id ID #REQUIRED status (omissis repealed suspended) #IMPLIED style CDATA #IMPLIED > ID and IDREF attributes are very important in our documents because of the large numbers of internal (and external) references contained in all of them. An ID attribute specifies that elements as an important element that may need to be identified individually. - The unique values across the document see to that An IDREF attribute creates a connection between an element and an important one (e.g. a reference between a note marker and a note) - The existence of the corresponding ID value is required Next: Attribute specification: examples 21/33 Next: Parameter entities: <!ENTITY % > 22/33 Parameter entities: <!ENTITY % > Definition: <!ENTITY % name "value"> Use: %name; Many parts of the DTD are heavily repetitive. Parameter entities simplify the management of repeated fragments. All parts of a DTD can be specified in a parameter entity, but mostly they are used to define content models and attribute lists that are shared by multiple elements. <!ENTITY % HStruct "(meta,preamble?,clauses,attach?)" > <!ENTITY % cont "contains (Original Simple Multiple) 'Original'"> XML Schema <!ELEMENT act %HStruct; > <!ELEMENT bill %HStruct; > <!ATTLIST bill %cont; > Next: XML Schema 23/33 4

5 Modularity XML Schema - A sophisticated and complex mechanism for file-level modularity A sophisticated type hierarchy modeled after object-oriented programming languages to provide for construct-level modularity Namespace management - Namespaces are a controversial but ubiquitous characteristics of reallife XML projects XML Schema explicitly allows namespaces and freely qualified elements and attributes. DTDs cannot really handle namespaces. Improved constraints on elements and attributes - Types allow greater control on text values. Improved management of element structures and mixed content are also available. Explicit documentation - Schema fragments can be explcitly commented for easier reading XML Syntax - Makes for much longer files, but allow all sorts of different tools to be used on schemas (e.g. presentation and verification). Next: Types 25/33 Types All element content and attribute values must comply to constraints specified in types (more sophisticated than content models) Simple types - Simple strings that match constraints as to their values. Strings, integers, dates, times, URIs, etc predefined simple types that can be refined adding further constraints (such as allowed values, min and max length, etc.) Complex Types - Element structures that match constraints as to their containment. Similar to content models, but shared among differently named elements. - Same constraints as content models plus a few more functionalities for mixed content and sequencing). - No predefined types, but sophisticated mechanisms for customization Next: Defining elements and attributes 26/33 Defining elements and attributes <xsd:complextype name="doctypes" > <xsd:choice> <xsd:element name="act" type="hstruct"/> <xsd:element name="bill" type="hstruct"/> <xsd:element name="doc" type="hstruct"/> <xsd:element name="report" type="hstruct"/> </xsd:choice> </xsd:complextype> <xsd:element name="akomantoso" type="doctypes" /> <xsd:simpletype name="versiontype" > <xsd:restriction base="xsd:string"> <xsd:enumeration value="original" /> <xsd:enumeration value="single" /> <xsd:enumeration value="multiple" /> </xsd:restriction> </xsd:simpletype> <xsd:attribute name="contains" type="versiontype" default="original" /> Next: Mixed content model 27/33 Mixed content model XML schema allows any constraint on mixed content elements, as long as they allow text anywhere where elements can be. <xsd:element name="dummy" type="dummy1"/> <xsd:complextype name="dummy1" mixed="true"> <xsd:sequence> <xsd:element name="first" type="xsd:string"/> <xsd:element name="second" type="xsd:string"/> <xsd:element name="third" type="xsd:string"/> </xsd:sequence> </xsd:complextype> In this case, the content model requires a sequence of first, second and third, but they can have text anywhere. This cannot be done with DTDs. Next: XSLT 28/33 XSLT XSLT XSLT stands for Extensible Stylesheet Language, Transformation It is the most important mechanism for displaying XML documents (on paper or on browsers) The idea is to use XSLT to convert XML documents into something that can be understood by the presentation engine - For browsers, the language that all understand is XHTML, therefore XSLT convert XML documents into XHTML - For print, the most common language is XSL-FO (Formatting Object) that can be used to create PDF files. Each element of the XML file is associated to a rule that tells how to convert it into something visible. The collections of all rules is the XSLT document. Next: XSLT - an example 30/33 5

6 XSLT - an example <xsl:template match="ref"> <a> <xsl:apply-templates select="@href" /> <xsl:apply-templates /> </a> </xsl:template> Next After the break we shall do some exercises on: - The syntax of DTDs - The basic ideas of XML Schema - The fundamental concepts of XSLT Converts an Akoma Ntoso <ref> element into an XHTML <a href> element, which is a hypertext link for browsers. <xsl:apply-templates select="@href" /> selectes the href attribute and transforms it into another (slightly different) href attribute. The is from a special language, called XPath, that allows expressions to refer to the elements and attributes of an XML document. <xsl:apply templates/> tries to transform the content of the <ref> element by looking in the XSLT stylesheet for the most appropriate rule. Next: Next 31/33 Next: Conclusions 32/33 Conclusions Markup languages are necessary for enriching data with information about the usages and the applications that can use the data Descriptive markup is the best starting point for the creation of new markup languages. XML is best among markup languages for several reasons: - It is a non proprietary, widely accepted standard - It is structured, hierarchical, descriptive - It allows both prescriptive and descriptive approaches - Tools exist in all operating systems and computer architectures. Fine presentazione 33/33 6

- What we actually mean by documents (the FRBR hierarchy) - What are the components of documents

- What we actually mean by documents (the FRBR hierarchy) - What are the components of documents Purpose of these slides Introduction to XML for parliamentary documents (and all other kinds of documents, actually) Prof. Fabio Vitali University of Bologna Part 1 Introduce the principal aspects of electronic