copyright (c) [2000]. roger l. costello. all rights reserved. 1 xml schemas roger l

1Copyright (c) [2000]. Roger L. Costello. All Rights Reserved.

XML Schemas

http://www.w3.org/TR/xmlschema-1/ http://www.w3.org/TR/xmlschema-2/

Roger L. Costello

XML Technologies


Thanks

• Special thanks to the following people for their help in answering my endless barrage of questions:– Henry Thompson– Andrew Layman– Noah Mendelsohn

– David Beech– Rick Jelliffe

• Many thanks the following people who have carefully reviewed this tutorial and notified me of bugs, typos, etc.– Oliver Becker

– Kit Lueder– David Wang


Motivation• People are dissatisfied with DTDs

– It's not XML

• So, you write your XML document in one language and you specify the grammar of that document using another language (DTD) --> bad, inconsistent

– Limited datatype capability

• DTDs support a very limited capability for specifying datatypes. You can't, for example, say "I want this <elevation> element to be of datatype "int"

• Desire a set of datatypes compatible with those found in databases

– DTD supports 10 datatypes; XML Schemas supports 37+ datatypes


Highlights of XML Schemas• XML Schemas are a tremendous advancement over DTDs:

– Enhanced datatypes • 37+ versus 10• Can create your own datatypes• Can define the lexical representation

– Example "This element can contain strings of this form: ddd-dddd, where 'd' represents a 'digit'".

– Written in XML• enables use of XML tools

– Object-oriented• Can extend or restrict a type (derive new type definitions on the basis of old ones)

– Can express sets - the child elements may occur in any order– Can specify element content as being unique (keys on content) and uniqueness within a region– Can define multiple elements with the same name but different content– Can define elements with null content– Can create equivalent elements - e.g., the "subway" element is equivalent to the "train" element.


Problem

• Convert BookCatalogue.dtd to the XML Schema notation– for this first example we will make a straight,

one-to-one conversion, i.e., Title, Author, Date, ISBN, and Publisher will hold strings, just like is done in the DTD (next slide)

– We will gradually modify the example to give more custom types to these elements

BookCatalogue.dtd

<!ELEMENT BookCatalogue (Book)*><!ELEMENT Book (Title, Author, Date, ISBN, Publisher)><!ELEMENT Title (#PCDATA)><!ELEMENT Author (#PCDATA)><!ELEMENT Date (#PCDATA)><!ELEMENT ISBN (#PCDATA)><!ELEMENT Publisher (#PCDATA)>


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <element name="BookCatalogue"> <annotation> <info>A book catalogue contains zero or more books</info> </annotation> <type> <element ref="cat:Book" minOccurs="0" maxOccurs="*"/> </type> </element> <element name="Book"> <annotation> <info>A Book has a Title, Author, Date, ISBN, and a Publisher</info> </annotation> <type> <element ref="cat:Title"/> <element ref="cat:Author"/> <element ref="cat:Date"/> <element ref="cat:ISBN"/> <element ref="cat:Publisher"/> </type> </element> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/></schema>

BookCatalogue1.xsdxsd = Xml-Schema Definition

(explanations onsucceeding pages)



BookCatalogue1.xsd

This (default)namespacedeclarationsays that allthese elementscome from thisnamespace (theXML Schemanamespace).

By virtue of thefact that they areassociated withan element thatcomes from theXML Schemanamespace, theseattributes alsocome from theXML Schema namespace.(Recall that a default namespacedoesn’t apply to attributes.)



BookCatalogue1.xsd

Says that theelements andtypes definedin this schemaare in thisnamespace.This will beused in instancedocuments toindicate that theelements contained in theinstance document comefrom thisnamespace.



BookCatalogue1.xsd

Here we arereferencing aBook element.Where is thatBook elementdefined? In what namespace?The cat: prefixindicates whatnamespace thiselement is defined in. cat:has been set tobe the same as thetargetNamespace.


xmlns:cat

• The schema element has an attribute xmlns:cat. The cat: namespace prefix, as we noted, is used for one element referencing another element within the schema.

• Clearly, this attribute will be schema-dependent, e.g., if I write a schema for cars I might have xmlns:car.

• Obviously, there is no way for xml-schema.dtd to account for all the possibilities. Thus, in the schema we supplement xml-schema.dtd with the internal subset declaration:

<!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]>



BookCatalogue1.xsd

The annotation/info elements areoptional. Theircontent is intended forhuman consumption, i.e., it's a comment.


Referencing a schema in an XML instance document

<?xml version="1.0"?><BookCatalogue xmlns ="http://www.somewhere.org/BookCatalogue" xmlns:xsi="http://www.w3.org/1999/XMLSchema/instance" xsi:schemaLocation="http://www.somewhere.org/BookCatalogue http://www.somewhere.org/BookCatalogue/BookCatalogue1.xsd"> <Book> <Title>My Life and Times</Title> <Author>Paul McCartney</Author> <Date>July, 1998</Date> <ISBN>94303-12021-43892</ISBN> <Publisher>McMillin Publishing</Publisher> </Book> ...</BookCatalogue>

In the BookCatalogue element (the root element) I declare that the schemaLocation attributecomes from the XML Schema Instance namespace (xsi). The value of schemaLocation is apair of values - a namespace and the URI to a schema. When the XML parser processes thisXML document it will use the schemaLocation pair of values to determine the XML Schemathat it conforms to. It will retrieve the schema at the URI specified in schemaLocation (inthis example, BookCatalogue.xsd) and then it will open up this schema document to confirmthat its targetNamespace value matches the namespace value shown in schemaLocation. In this case it does. I declare (using a default namespace) that all the elements in this XMLinstance document comes from the same namespace.


Referencing a schema in an XML instance document

BookCatalogue.xml BookCatalogue.xsd

targetNamespace="A"schemaLocation="A A/BookCatalogue.xsd"

- defines elements for namespace A

- uses elements from namespace A


Note about schemaLocation

• schemaLocation is just a hint to the XML Parser• "The choice of which schema to use ultimately lies with the

consumer. If you as a consumer wish to rely on the schemaLocation idiom, then you should purchase/use processors that will honor that for you. The reason that some other processors might not provide that service to you is that they are designed to run in environments where it is impractical or undesirable to allow the document author to force reference to and use of some particular schema document." (Noah Mendelsohn)

• For this tutorial I will assume that we are using an XML Parser which uses the schemaLocation idiom.


Note multiple levels of checking

BookCatalogue.xml BookCatalogue1.xsd xml-schema.dtd

Does the xml documentconform to the rules laidout in the xml-schema?

Is the xml-schema a validxml document, i.e., does itconform to the rules laidout in the xml-schema DTD?

Do Lab1


Alternate Schema

• On the following slide is an alternate (equivalent) way of representing the schema shown previously.


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <element name="BookCatalogue"> <type> <element name="Book" minOccurs="0" maxOccurs="*"> <type> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type> </element> </type> </element></schema>

BookCatalogue2.xsd


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <element name="BookCatalogue"> <type> <element name="Book" minOccurs="0" maxOccurs="*"> <type> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type> </element> </type> </element></schema>

BookCatalogue2.xsd

Anonymous type (no name)

Do Lab 2


Named Types

• The following slide shows an alternate (equivalent) schema which uses named types.


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <element name="BookCatalogue"> <type> <element name="Book" minOccurs="0" maxOccurs="*" type="cat:CardCatalogueEntry"/> </type> </element> <type name="CardCatalogueEntry"> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type></schema>

BookCatalogue3.xsd


Problem

• Defining the Date element to be of type string is unsatisfactory (it allows any string value to be input as the content of the Date element, including non-date strings). We would like to constrain the allowable content that Date can have. Modify the XML-Schema to restrict the content of the Date element to just date values.

• Similarly, constrain the content of the ISBN element to content of this form: ddddd-ddddd-ddddd or d-ddd-ddddd-d or d-dd-dddddd-d, where 'd' stands for 'digit'


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <datatype name="ISBNType" source="string"> <pattern value="\d{5}-\d{5}-\d{5}"/> <pattern value="\d{1}-\d{3}-\d{5}-\d{1}"/> <pattern value="\d{1}-\d{2}-\d{6}-\d{1}"/> </datatype> <element name="BookCatalogue"> <type> <element name="Book" minOccurs="0" maxOccurs="*"> <type> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="date"/> <element name="ISBN" type="cat:ISBNType"/> <element name="Publisher" type="string"/> </type> </element> </type> </element></schema>

BookCatalogue4.xsd


<datatype name="ISBNtype" source="string"> <pattern value="\d{5}-\d{5}-\d{5}"/> <pattern value="\d{1}-\d{3}-\d{5}-\d{1}"/> <pattern value="\d{1}-\d{2}-\d{6}-\d{1}"/></datatype>

"Elements of this datatype will have string content. The stringmust conform to one of the three patterns listed. - The first pattern is: 5 digits followed by a dash followed by 5 digits followed by another dash followed by 5 more digits.- The second pattern is: 1 digit followed by a dash followed by 3 digits followed by another dash followed by 5 digits followed by another dash followed by 1 more digit.- The third pattern is: 1 digit followed by a dash followed by 2 digits followed by another dash followed by 6 digits followed by another dash followed by 1 more digit."

These patterns are specified using Regular Expressions. In a few slideswe will see more of the Regular Expression syntax.


Built-in Datatypes

• Primitive Datatypes

– string

– boolean

– float

– double

– decimal

– timeInstant

– timeDuration

– recurringInstant

– binary

– uri

• Atomic, built-in

– "Hello World"

– {true, false}

– 12.56E3, 12, 12560, 0, -0, INF, -INF, NAN – 12.56E3, 12, 12560, 0, -0, INF, -INF, NAN

– 7.08

– 1999-12-04T20:12:00.000

– 1Y2M3DT10H30M12.3S

– same format as timeInstant

– 010010111001

– http://www.somewhere.org

Note: 'T' is the date/time separator INF = infinity NAN = not-a-number


Built-in Datatypes (cont.)• Generated datatypes

– language – NMTOKEN– NMTOKENS– Name– NCName– QNAME– ID– IDREF– IDREFS– ENTITY– ENTITIES– NOTATION– integer– non-negative-integer– positive-integer– non-positive-integer– negative-integer– date– time

• Subtype of primitive datatype– any valid xml:lang value, e.g., EN, FR, ... – "house"– "house barn yard"– "hello-there"– part (no namespace qualifier)– book:part– Token, must be unique– Token which matches an ID– List of IDREF

– 456– zero to infinity– one to infinity– negative infinity to zero– negative infinity to negative one– 1999-05-21– 13:20:00.000

Do Lab 3


Creating your own Datatypes

• We can create new datatypes from existing datatypes (called source or basetype) by specifying values for one or more of the optional facets

• Example. The string primitive datatype has nine optional facets - pattern, enumeration, length, maxlength, maxInclusive, maxExclusive, minlength, minInclusive and minExclusive.


Example

<datatype name="TelephoneNumber" source="string"> <length value="8"/> <pattern value="\d{3}-\d{4}"/></datatype>

This creates a new datatype called 'TelephoneNumber'.Elements of this type can hold string values, but thestring length must be exactly 8 characters long and thestring must follow the pattern: ddd-dddd, where 'd' represents a 'digit'.


Facets of the Integer Datatype

• Facets:– maxInclusive– maxExclusive– minInclusive– minExclusive


Example

<datatype name= "EarthSurfaceElevation" source="integer"> <minInclusive value="-1246"/> <maxInclusive value="29028"/></datatype>

This creates a new datatype called 'EarthSurfaceElevation'.Elements of this type can hold an integer.However, the integer must have a valuebetween -1246 and 29028, inclusive.


General Form of Datatype/Facet Usage

<datatype name= "name" source= "source"> <facet value= "value"/> <facet value= "value"/> ...</datatype>

Facets: - minInclusive - maxInclusive - minExclusive - maxExclusive - length - minlength - maxlength - pattern - enumeration ...

Sources: - string - boolean - float - double - decimal - timeInstant - timeDuration - recurringInstant - binary - uri ...

Do Lab 4


Regular Expressions

• Recall that the string datatype has a pattern facet. The value of a pattern facet is a regular expression. Below are some examples of regular expressions:

Regular Expression - Chapter \d - a*b - [xyz]b - a?b - a+b - [a-c]x

Example - Chapter 1 - b, ab, aab, aaab, … - xb, yb, zb - b, ab - ab, aab, aaab, … - ax, bx, cx


Regular Expressions (cont.)

• Regular Expression– [a-c]x– [-ac]x– [ac-]x– [^0-9]x– \Dx– Chapter\s\d– (ho){2} there– (ho\s){2} there– .abc– (a|b)+x

• Example– ax, bx, cx

– -x, ax, cx

– ax, cx, -x– any non-digit char followed by x

– any non-digit char followed by x

– Chapter followed by a blank followed by a digit

– hoho there

– ho ho there– any char followed by abc

– ax, bx, aax, bbx, abx, bax,...


Regular Expressions (cont.)

• a{1,3}x• a{2,}x• \w\s\w

• ax, aax, aaax• aax, aaax, aaaax, …• word (alphanumeric

plus dash) followed by a space followed by a word


Example R.E.

[1-9]?[0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5]

0 to 99 100 to 199 200 to 249 250 to 255

This regular expression restricts a string to havevalues between 0 and 255.… Such a R.E. might be useful in describing anIP address ...


IP Datatype Definition<datatype name="IP" source="string"> <pattern value="(([1-9]?[0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\.){3} ([1-9]?[0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])"> <annotation> <info> Datatype for representing IP addresses. Examples, 129.83.64.255, 64.128.2.71, etc. This datatype restricts each field of the IP address to have a value between zero and 255, i.e., [0-255].[0-255].[0-255].[0-255] Note: in the value attribute (above) the regular expression has been split over two lines. This is for readability purposes only. In practice the R.E. would all be on one line. </info> </annotation> </pattern></datatype>


Regular Expression Parser

• Want to test your skill in writing regular expressions? Go to: http://www.xfront.org/xml-schema/– Dan Potter has created a nice tool which allows

you to enter a regular expression and then enter a string. The parser will then determine if your string conforms to your regular expression.

Do Lab 5


Derived Types

• We can do a form of subclassing the type definitions. We call this "derived types"– derive by extension: extend the parent type with

more elements– derive by restriction: constrain the parent type

by constraining some of the elements to have a more restricted range of values, or a more restricted number of occurrences.


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <type name="Publication"> <element name="Title" type="string" maxOccurs="*"/> <element name="Author" type="string" maxOccurs="*"/> <element name="Date" type="date"/> </type> <type name="Book" source="cat:Publication" derivedBy="extension"> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type> <element name="BookCatalogue"> <type> <element name="CatalogueEntry" minOccurs="0" maxOccurs="*" type="cat:Book"/> </type> </element></schema>

BookCatalogue5.xsd


<type name="Publication"> <element name="Title" type="string" maxOccurs="*"/> <element name="Author" type="string" maxOccurs="*"/> <element name="Date" type="date"/></type><type name="Book" source="cat:Publication" derivedBy="extension"> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/></type>

Elements of type Book will have 5 child elements - Title, Author, Date, ISBN, and Publisher.


Using Derived Types

• If we declare an element to be of type Publication then in the XML instance document that element's content can be either a Publication or a Book (since Book is a Publication).


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Catalogue" xmlns:cat="http://www.somewhere.org/Catalogue"> <type name="Publication"> <element name="Title" type="string" maxOccurs="*"/> <element name="Author" type="string" maxOccurs="*"/> <element name="Date" type="date"/> </type> <type name="Book" source="cat:Publication" derivedBy="extension"> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type> <element name="Catalogue"> <type> <element name="CatalogueEntry" minOccurs="0" maxOccurs="*" type="cat:Publication"/> </type> </element></schema>

BookCatalogue6.xsd


<?xml version="1.0"?><Catalogue xmlns ="http://www.somewhere.org/Catalogue" xmlns:xsi="http://www.w3.org/1999/XMLSchema/instance" xsi:schemaLocation="http://www.somewhere.org/Catalogue http://www.somewhere.org/Catalogue/BookCatalogue6.xsd"> <CatalogueEntry> <Title>Staying Young Forever</Title> <Author>Karin Granstrom Jordan, M.D.</Author> <Date>December, 1999</Date> </CatalogueEntry> <CatalogueEntry xsi:type="Book"> <Title>Illusions The Adventures of a Reluctant Messiah</Title> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Publisher>Dell Publishing Co.</Publisher> </CatalogueEntry> <CatalogueEntry xsi:type="Book"> <Title>The First and Last Freedom</Title> <Author>J. Krishnamurti</Author> <Date>1954</Date> <ISBN>0-06-064831-7</ISBN> <Publisher>Harper & Row</Publisher> </CatalogueEntry></Catalogue>

BookCatalogue2.xml


<CatalogueEntry xsi:type="Book"> <Title>Illusions The Adventures of a Reluctant Messiah</Title> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Publisher>Dell Publishing Co.</Publisher></CatalogueEntry>

"The CatalogueEntry element is declared to be of type Publication. Bookis derived from Publication. Therefore, Book is a Publication. Thus, thecontent of CatalogueEntry can be a Book. However, to indicate that the content is not the source type, but rather a derived type, we need to specifythe derived type that is being used. The attribute 'type' comes from theXML Schema Instance (xsi) namespace."


Why is xsi:type Needed?

• Why, in an instance document, do we need to indicate the derived type being used?

• Suppose that there are several types derived (by extension) from Publication, and some of the extended element declarations are optional. In the instance document, if xsi:type was not used, it might get very difficult for an XML Parser to determine which derived type is being used.

Do Lab 6


Derive by Restriction<type name="Publication"> <element name="Title" type="string" maxOccurs="*"/> <element name="Author" type="string" maxOccurs="*"/> <element name="Date" type="date"/></type><type name= "SingleAuthorPublication" source="cat:Publication" derivedBy= "restriction"> <restrictions> <element name="Author" type="string" maxOccurs="1"/> </restrictions></type>

Elements of type SingleAuthorPublication will have 3 child elements - Title, Author, and Date.There must be exactly one Author element.


Restricting Derivations

• Sometimes we may want to create a type and disallow all derivations of it, or just disallow extensions of it, or restrictions of it.

<type name="Publication" final="#all" …> This type cannot be extended nor restricted

<type name="Publication" final="restriction" …> This type cannot be restricted

<type name="Publication" final="extended" …> This type cannot be extended


exact Types

• If you define a type to be exact, then other types may derive from it. However, in the instance document derived types may not be used in its stead.


<type name="Publication"> <element name="Title" type="string" maxOccurs="*"/> <element name="Author" type="string" maxOccurs="*"/> <element name="Date" type="date"/> </type> <type name="Book" source="cat:Publication" derivedBy="extension"> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type> <element name="Catalogue"> <type> <element name="CatalogueEntry" minOccurs="0" maxOccurs="*" type="cat:Publication"/> </type> </element>

<CatalogueEntry xsi:type="Book"> <Title>Illusions The Adventures of a Reluctant Messiah</Title> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Publisher>Dell Publishing Co.</Publisher> </CatalogueEntry>

Schema:

Instance doc:

This permits Publication elements, as well as types derived from Publicationto be used as a child of Catalogue, e.g., Book


<type name="Publication" exact="extension"> <element name="Title" type="string" maxOccurs="*"/> <element name="Author" type="string" maxOccurs="*"/> <element name="Date" type="date"/> </type> <type name="Book" source="cat:Publication" derivedBy="extension"> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type> <element name="Catalogue"> <type> <element name="CatalogueEntry" minOccurs="0" maxOccurs="*" type="cat:Publication"/> </type> </element>

<CatalogueEntry xsi:type="Book"> <Title>Illusions The Adventures of a Reluctant Messiah</Title> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Publisher>Dell Publishing Co.</Publisher> </CatalogueEntry>

Schema:

Instance doc:

This prohibits the use of types derived by extension to be used as children of CatalogueEntry, e.g., this is not allowed


exact Types

• exact="extension"– Prohibits types derived by extension to be used in its

stead in instance documents

• exact="restriction"– Prohibits types derived by restriction to be used in

its stead in instance documents

• exact="#all"– Prohibits all derived types to be used in its stead in

instance documents


Equivalence

• Oftentimes in daily conversation there are several ways to express something.

– In Boston we use the words "T" and "subway" interchangeably. For example, "we took the T into town", or "we took the subway into town".

• Thus, "T" and "subway" are equivalent. Which one is used may depend upon what part of the state you live in, what mood you're in, or any number of factors.

• We would like to be able to express this "equivalence" capability in XML Schemas.

– We would like to be able to declare in the schema an element called "subway", an element called "T", and state that "T" is equivalent to "subway". Thus, instance documents can use either "subway" or "T", depending on their preference.


equivClass

• We can create an element (called the exemplar) and then create other elements which state that they are equivalent to the exemplar.

<element name="subway" type="string"/> <element name="T" equivClass="boston:subway" type="string"/>

subway is the exemplarT is equivalent.

So what's the big deal? - Where ever the exemplar can be used in an instance document, any equivalent element can also be used!


<element name="subway" type="string"/> <element name="T" equivClass="boston:subway" type="string"/> <element name="transportation"> <type> <element ref="boston:subway"/> </type> </element>

<transportation> <subway>Red Line</subway> </transportation>

Schema:

Instance doc:

Note: the type of every element of an equivalence class must be the same as or derivedfrom the type of the exemplar element.

<transportation> <T>Red Line</T> </transportation>

Alternative Instance doc:


Enabling Interoperability

• One very hard problem in today's world is how to enable different domains to communicate effectively when they don't all speak the same language.

• The equivClass is a good step towards enabling interoperability.– It makes explicit the equivalence of one

element with another element.


Enabling Interoperability

• Imagine that you create an application. The application is designed to input XML documents. Suppose that within the XML document the application expects to see a <subway> element.

• Now suppose that it receives an XML document, but it contains a <T> element.

• The application can go to the XML Schema and see that <T> is equivalent to <subway>. Thus, it accepts and understands the XML document, even though it is using a different vocabulary than what the application was written to. Wow!

• Further, over time new element declarations can be added to the schema. For example, <element name="train" equivClass="boston:subway" type="string"/>

• Without any change to the application, the application will be able to process XML documents with a <train> element by simply consulting the schema.

• Mike Los coined the term "interoperability schema" to describe schemas used in the fashion described above.

Do Lab 7


Abstract Elements

• You can declare an element to be abstract– Example. <element name="Publication" type="cat:Pub" abstract="true"/>

• An abstract element is a kind of template/placeholder.• If an element is abstract then in the XML instance

document that element may not appear.– Example. <Publication> may not appear in an

instance document.• However, elements that are equivalent to the abstract

type may appear in its place.


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Catalogue" xmlns:cat="http://www.somewhere.org/Catalogue"> <type name="Pub"> <element name="Title" type="string" maxOccurs="*"/> <element name="Author" type="string" maxOccurs="*"/> <element name="Date" type="date"/> </type> <element name="Publication" type="cat:Pub" abstract="true"/> <element name="Book" equivClass="cat:Publication"> <type source="cat:Pub" derivedBy="extension"> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </type> </element> <element name="Magazine" equivClass="cat:Publication"> <type source="cat:Pub" derivedBy="restriction"> <restrictions> <element name="Author" type="string" maxOccurs="0"/> </restrictions> </type> </element> <element name="Catalogue"> <type> <element ref="cat:Publication" minOccurs="0" maxOccurs="*"/> </type> </element></schema>

BookCatalogue7.xsd

Since the Publicationelement is abstract,only equivalentelements can appearas children of Catalogue.

The Book andMagazine elementsare equivalent to thePublication element.


<?xml version="1.0"?><Catalogue xmlns ="http://www.somewhere.org/Catalogue" xmlns:xsi="http://www.w3.org/1999/XMLSchema/instance" xsi:schemaLocation="http://www.somewhere.org/Catalogue http://www.somewhere.org/Catalogue/BookCatalogue7.xsd"> <Magazine> <Title>Natural Health</Title> <Date>December, 1999</Date> </Magazine> <Book> <Title>Illusions The Adventures of a Reluctant Messiah</Title> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Publisher>Dell Publishing Co.</Publisher> </Book> <Book> <Title>The First and Last Freedom</Title> <Author>J. Krishnamurti</Author> <Date>1954</Date> <ISBN>0-06-064831-7</ISBN> <Publisher>Harper & Row</Publisher> </Book></Catalogue>

BookCatalogue3.xml

An XML Instance Document of BookCatalogue7.xsd


Attributes

• On the next slide I show a version of the BookCatalogue DTD that uses attributes. On the following slide I show how this is implemented using XML Schemas.

<!ELEMENT BookCatalogue (Book)*><!ELEMENT Book (Title, Author+, Date, ISBN, Publisher)><!ATTLIST Book Category (autobiography | non-fiction | fiction) #REQUIRED InStock (true | false) ”false" Reviewer CDATA ""><!ELEMENT Title (#PCDATA)><!ELEMENT Author (#PCDATA)><!ELEMENT Date (Month?, Year)><!ELEMENT ISBN (#PCDATA)><!ELEMENT Publisher (#PCDATA)><!ELEMENT Month (#PCDATA)><!ELEMENT Year (#PCDATA)>

BookCatalogue2.dtd


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <element name="BookCatalogue"> <annotation> <info>A book catalogue contains zero or more books</info> </annotation> <type> <element ref="cat:Book" minOccurs="0" maxOccurs="*"/> </type> </element> <element name="Book"> <annotation> <info>A Book has a Title, one or more Authors, a Date, an ISBN, and a Publisher</info> </annotation> <type> <element ref="cat:Title"/> <element ref="cat:Author" maxOccurs="*"/> <element ref="cat:Date"/> <element ref="cat:ISBN"/> <element ref="cat:Publisher"/> <attributeGroup ref="BookAttributes"/> </type> </element>

cont. --->


<attributeGroup name="BookAttributes"> <annotation> <info> A Book has three attributes - Category, InStock, and Reviewer. Category must be either "autobiography", "non-fiction", or "fiction". A value must be supplied for this attribute whenever a Book element is used within a document. InStock can be either "yes" or "no". If no value is supplied it defaults to "no". Reviewer contains the name of the reviewer. It defaults to "" if no value is supplied. </info> </annotation> <attribute name="Category" minOccurs="1"> <datatype source="string"> <enumeration value="autobiography"/> <enumeration value="non-fiction"/> <enumeration value="fiction"/> </datatype> </attribute> <attribute name="InStock" type="boolean" default="false"/> <attribute name="Reviewer" type="string" default=""/> </attributeGroup> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/></schema>

BookCatalogue8.xsd


<attribute name="Category" minOccurs="1"> <datatype source="string"> <enumeration value="autobiography"/> <enumeration value="non-fiction"/> <enumeration value="fiction"/> </datatype></attribute>

"The default value for maxOccurs is 1. Thus, this attributeis REQUIRED."


Alternate Schema

• On the next slide is another way of expressing the last example.


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <element name="BookCatalogue"> <type> <element name="Book" minOccurs="0" maxOccurs="*"> <type> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> <attribute name="Category" minOccurs="1"> <datatype source="string"> <enumeration value="autobiography"/> <enumeration value="non-fiction"/> <enumeration value="fiction"/> </datatype> </attribute> <attribute name="InStock" type="boolean" default="false"/> <attribute name="Reviewer" type="string" default=""/> </type> </element> </type> </element></schema>

BookCatalogue9.xsd


Note about Attributes

• The attribute declarations always come last, after the element declarations.

Do Lab 8


group Element

• The group element enables you to group together element declarations.

• Note: the group element is just for grouping together element declarations, no attribute declarations allowed.


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:cat CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/BookCatalogue" xmlns:cat="http://www.somewhere.org/BookCatalogue"> <element name="BookCatalogue"> <type> <element name="Book" minOccurs="0" maxOccurs="*"> <type> <group ref="cat:BookElements"/> <attribute name="Category" minOccurs="1"> <datatype source="string"> <enumeration value="autobiography"/> <enumeration value="non-fiction"/> <enumeration value="fiction"/> </datatype> </attribute> <attribute name="InStock" type="boolean" default="false"/> <attribute name="Reviewer" type="string" default=""/> </type> </element> </type> </element> <group name="BookElements" order="seq"> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </group></schema>

BookCatalogue10.xsd


Expressing Alternates

<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:sig CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples" xmlns:sig="http://www.somewhere.org/Examples"> <element name="signature"> <type> <group order="choice"> <element ref="sig:name"/> <group order="seq"> <element ref="sig:name"/> <element name="date" type="date"/> </group> </group> </type> </element> <element name="name" type="string"/></schema>

<!ELEMENT signature (name | (name, date))>DTD:

XML Schema:


Expressing Repeats

<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:bi CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples" xmlns:bi="http://www.somewhere.org/Examples"> <element name="binary-digit"> <type> <group order="choice" maxOccurs="*"> <element name="zero" type="bi:zero-digit"/> <element name="one" type="bi:one-digit"/> </group> </type> </element> <datatype name="zero-digit" source="string"> <enumeration value="0"/> </datatype> <datatype name="one-digit" source="string"> <enumeration value="1"/> </datatype></schema>

<!ELEMENT binary-digit (zero | one)*>DTD:

XML Schema:


Expressing Any Order

<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples"> <element name="Book"> <type> <group order="all"> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="date"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> </group> </type> </element></schema>

XML Schema:

Problem: create an element, Book, which contains Author, Title, Date, ISBN, and Publisher, in any order (Note: this cannot be done with DTDs).

order="all" means that Book must contain all five child elements, but they may occur in any order.Note: minOccurs, maxOccurs are both fixed to a value of "1".

Do Lab 9


Empty Element

<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples"> <element name="image"> <type content="empty"> <attribute name="href" type="uri"/> </type> </element></schema>

<image href="http://www.xfront.org/Rog.gif"/>

Schema:

Instancedoc:

Do Lab 10


Uniqueness

• DTDs provided the ID attribute datatype for uniqueness (i.e., an ID value must be unique throughout the entire document, and the XML parser enforces this).

• XML Schema has much enhanced uniqueness capabilities:

– enables you to define element content to be unique.

– enables you to define non-ID attributes to be unique.

– enables you to define a combination of element content and attributes to be unique.

– enables you to distinguish between unique and key.

– enables you to declare the range of the document over which something is unique


unique vs key

• Key: an element/attribute (or combination thereof) which is defined to be a key must – always be present (minOccurs must be greater

than zero)– be non-nullable (i.e., nullable="false")– be unique

• Key implies unique, but unique does not imply key


<?xml version="1.0"?><Library xmlns="http://www.somewhere.org/Library"> <BookCatalogue> <Book Category = "fiction" InStock = "yes" Reviewer = "John Doe"> <Title>Illusions The Adventures of a Reluctant Messiah</Title> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Publisher>Dell Publishing Co.</Publisher> </Book> <Book Category = "non-fiction" InStock = "yes" Reviewer = "John Doe"> <Title>The First and Last Freedom</Title> <Author>J. Krishnamurti</Author> <Date>1954</Date> <ISBN>0-06-064831-7</ISBN> <Publisher>Harper & Row</Publisher> </Book> </BookCatalogue> <CheckoutRegister> <Person>Roger Costello</Person> <Book titleRef="Illusions The Adventures of a Reluctant Messiah" categoryRef="fiction"/> </CheckoutRegister></Library>

+ = key

+ = keyref


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:lib CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Library" xmlns:lib="http://www.somewhere.org/Library"> <element name="Library"> <type> <element name="BookCatalogue"> <type> <element name="Book" minOccurs="0" maxOccurs="*"> <type> <element name="Title" type="string"/> <element name="Author" type="string"/> <element name="Date" type="string"/> <element name="ISBN" type="string"/> <element name="Publisher" type="string"/> <attribute name="Category" minOccurs="1"> <datatype source="string"> <enumeration value="autobiography"/> <enumeration value="non-fiction"/> <enumeration value="fiction"/> </datatype> </attribute> <attribute name="InStock" type="boolean" default="false"/> <attribute name="Reviewer" type="string" default=""/> </type> </element> </type> </element>


<element name="CheckoutRegister"> <type> <element name="Person" type="string"/> <element name="Book"> <type content="empty"> <attribute name="titleRef" type="string"/> <attribute name="categoryRef" type="string"/> </type> </element> </type> </element> </type> </element> <key name="bookKey"> <selector>Library/BookCatalogue/Book</selector> <field>Title</field> <field>@Category</field> </key> <keyref name="bookRef" refer="bookKey"> <selector>Library/CheckoutRegister/Book</selector> <field>@titleRef</field> <field>@categoryRef</field> </keyref></schema>

BookCatalogue11.xsd


Defining a Key<key name="bookKey"> <selector>Library/BookCatalogue/Book</selector> <field>Title</field> <field>@Category</field></key>

"I define that the combination of the contents of Title plus the valueof the attribute Category is to be unique throughout an XML instancedocument. The Title element and Category attribute lie withinthe XPath expression shown in the selector element."

Note: you can have one or more field elements. The key will be the combinationof all the fields.


Defining a Reference to a Key

<keyref name="bookRef" refer="bookKey"> <selector>Library/CheckoutRegister/Book</selector> <field>@titleRef</field> <field>@categoryRef</field><keyref>

"I define that the values in the two attributes, titleRef and categoryRef,combined, are a reference to a key defined by bookKey. The twoattributes are located at the XPath expression found in the selectorelement."

Note: if there are 2 fields in the key, then there must be 2 fields in the keyref,if there are 3 fields in the key, then there must be 3 fields in the keyref, etc.Further, the fields in the keyref must match in type and position to the key.


Defining Uniqueness<unique name="bookUnique"> <selector>Library/BookCatalogue/Book</selector> <field>Title</field> <field>@Category</field></unique>

"I define that the combination of the contents of Title plus the valueof the attribute Category is to be unique throughout an XML instancedocument. The Title element and Category attribute lie withinthe XPath expression shown in the selector element."


Specifying scope of uniqueness in XML Schemas?

- The key/keyref/unique elements may be placed anywhere in your schema.

- Where you place them determines the scope of the uniqueness.

- In our example we placed the key/keyref elements at the top-level (direct child of the schema element). Thus, we are stating that in an instance document the uniqueness is with respect to the entire document.

- On the other hand, if we were to place the key/keyref elements as a child of the Book element then the uniqueness will have a scope of just the Book element. Thus, over the entire instance document there may be repeats, but within any Book element it will be unique.


any Element

• The any element allows any well-formed XML.

<element name="free-form"> <type> <any/> </type></element>

The free-form element can contain any well-formed XML (WFXML)."

<free-form> <comment source="Roger">This is great!</comment></free-form>


anyAttribute

• The anyAttribute allows any attribute

<element name="free-form"> <type content="empty"> <anyAttribute/> </type></element>

The free-form element can have any attribute.

<free-form comment="This is great"/>


(Almost) any Element/Attribute

<any namespace="##other"/> allows any well-formed XML element, provided the element is in another namespace than the one we're defining.

<any namespace="http://www.somewhere.com"/> allows any well-formed XML element, provided it's from the specified namespace.

<any namespace="##targetNamespace"/> allows any well-formed XML element, provided it's from the namespace that we're defining.

<anyAttribute namespace="##other"/> allows any attribute, provided the attribute is in another namespace than the one we're defining.

<anyAttribute namespace="http://www.somewhere.com"/> allows any attribute, provided it's from the specified namespace.

<anyAttribute namespace="##targetNamespace"/> allows any attribute, provided it's from the namespace that we're defining.


Validating an XML Instance Document

• Validation can apply to the entire XML instance document, or to a single element.


<Library xmlns:book="http://www.somewhere.org/Examples" xmlns:person="http://www.somewhere-else.org/Person" xmlns:xsi="http://www.w3.org/1999/XMLSchema/instance" xsi:schemaLocation= "http://www.somewhere.org/Examples http://www.somewhere.org/ Examples/Book.xsd http://www.somewhere-else.org/Person http://www.somewhere-else.org/Person/Person.xsd"> <BookCatalogue> <book:Book> <book:Title>Illusions The Adventures of a Reluctant Messiah</book:Title> <book:Author>Richard Bach</book:Author> <book:Date>1977</book:Date> <book:ISBN>0-440-34319-4</book:ISBN> <book:Publisher>Dell Publishing Co.</book:Publisher> </book:Book> <book:Book> <book:Title>The First and Last Freedom</book:Title> <book:Author>J. Krishnamurti</book:Author> <book:Date>1954</book:Date> <book:ISBN>0-06-064831-7</book:ISBN> <book:Publisher>Harper & Row</book:Publisher> </book:Book> </BookCatalogue> <Employees> <person:Employee> <person:Name>John Doe</person:Name> <person:SSN>123-45-6789</person:SSN> </person:Employee> <person:Employee> <person:Name>Sally Smith</person:Name> <person:SSN>000-11-2345</person:SSN> </person:Employee> </Employees></Library>

Library.xml

Validating usingtwo schemas


Assembling a Schema from Multiple Schema Documents

• The include element allows you to bring in schema definitions from other schema– They must all have the same namespace– The net effect of include is as though you had typed all the definitions in

directly into the containing schema

<schema …> <include schemaLocation="Book.xsd"/> <include schemaLocation="Person.xsd"/> …</schema>

Book.xsd Person.xsd

Library.xsd


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"[<!ATTLIST schema xmlns:lib CDATA #IMPLIED>]><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples" xmlns:lib="http://www.somewhere.org/Examples"> <include schemaLocation="http://www.somewhere.org/Examples/Book.xsd"/> <include schemaLocation="http://www.somewhere.org/Examples/Person.xsd"/> <element name="Library"> <type> <element name="BookCatalogue"> <type> <element ref="lib:Book" minOccurs="0" maxOccurs="*"/> </type> </element> <element name="Employees"> <type> <element name="lib:Employee" minOccurs="0" maxOccurs="*"/> </type> </element> </type> </element></schema>

Library.xsd


import Element

• The import element allows you to reference elements in another namespace

<schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples" xmlns:html="http://www.w3.org/1999/XHTML"> <import namespace="http://www.w3.org/1999/XHTML" schemaLocation="http://www.w3.org/XHTML/xhtml.xsd"/> ... <element ref="html:table"> …</schema>


Declaration vs Definition

• You make declarations of things that will be used in an XML instance document.

• You make definitions of things that are just used in the schema document; a definition creates a new type

Declarations:- element declarations- attribute declarations

Definitions:- type definitions- attribute group definitions- model group definitions


Symbol Space

• Each type definition creates a new symbol space• Top-level element declarations are in the top-level

symbol space


<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples"> <element name="title" type="string"/> <type name="ChapterType"> <element name="title" type="string"/> </type> <type name="SectionType"> <element name="title" type="string"/> </type></schema>

3 different titles


Version Management

• The schema element has an optional attribute, version, which you may use to indicate the version of your schema (for private version documentation of the schema)

<?xml version="1.0"?><!DOCTYPE schema SYSTEM "xml-schema.dtd"><schema xmlns="http://www.w3.org/1999/XMLSchema" targetNamespace="http://www.somewhere.org/Examples" version="1.0"> ...</schema>


<type> or <datatype>?

• When do you use the type element and when do you use the datatype element?– Use the type element when there are elements

and/or attributes– Use the datatype element when it is a primitive

type (string, integer, etc)


null Content

• You can indicate in a schema that an element may be null in the instance document. Empty content vs null:

– Empty: an element with a type of content="empty" is constrained to have no content.

– null: an instance document element may indicate no value is available by setting an attribute - xsi:null - equal to 'true'

<element name="PersonName"> <type> <element name="forename" type="NMTOKEN"/> <element name="middle" type="NMTOKEN" nullable="true"/> <element name="surname" type="NMTOKEN"/> </type></element>

<PersonName> <forename>John</forename> <middle xsi:null="true"/> <surname>Doe</surname></PersonName>

XML Schema:

XML instancedocument:

The content of middle canbe a NMTOKEN value or,we can indicate that itscontent is undefined.


ur-type

• The ur-type is the source for all types which do not specify a value for the source attribute. It is the type for all elements which do not specify a type.– Example: <element name="foo"/>

<type name="ur-type" content="mixed"> <any min="0" max="*"/> <anyAttribute/></type>