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VALIDATING AN XML DOCUMENT

TUTORIAL 3. VALIDATING AN XML DOCUMENT. CREATING A VALID DOCUMENT. You validate documents to make certain necessary elements are never omitted. For example, each customer order should include a customer name, address, and phone number. CREATING A VALID DOCUMENT.

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VALIDATING AN XML DOCUMENT

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  1. TUTORIAL 3 VALIDATING AN XML DOCUMENT New Perspectives on XML, 2nd Edition Tutorial 3

  2. CREATING A VALID DOCUMENT • You validate documents to make certain necessary elements are never omitted. • For example, each customer order should include a customer name, address, and phone number. New Perspectives on XML, 2nd Edition Tutorial 3

  3. CREATING A VALID DOCUMENT • Some elements and attributes may be optional, for example an e-mail address. • An XML document can be validated using either • DTD (Document Type Definition) • Older, simplier language for describing how to render HTML and XML documents • Schema • Newer, more complex language for describing how to render XML documents New Perspectives on XML, 2nd Edition Tutorial 3

  4. CUSTOMER INFORMATION COLLECTED BY KRISTEN This figure shows customer information collected by Kristen Could this information be stored in a relational database? New Perspectives on XML, 2nd Edition Tutorial 3

  5. THE STRUCTURE OF KRISTEN’S DOCUMENT This figure shows the overall structure of Kristen’s document ? = zero or one time = exactly one time + = one or more times * = zero or more times “Red” indicates correction New Perspectives on XML, 2nd Edition Tutorial 3

  6. DECLARING A DTD • A DTD can be used to: • Ensure all required elements are present in the document • Prevent undefined elements from being used • Enforce a specific data structure • Specify the use of attributes and define their possible values • Define default values for attributes • Describe how the parser should access non-XML or non-textual content New Perspectives on XML, 2nd Edition Tutorial 3

  7. DECLARING A DTD • There can only be one DTD per XML document. • A DTD is a collection of rules or declarations that define the content and structure of the document. • A document type declaration attaches those rules to the document’s content. New Perspectives on XML, 2nd Edition Tutorial 3

  8. DECLARING A DTD • You create a DTD by first entering a document type declaration into your XML document. • DTD in this tutorial will refer to document type definition and not the declaration. • While there can only be one DTD, it can be divided into two parts: an internal subset and an external subset. New Perspectives on XML, 2nd Edition Tutorial 3

  9. DECLARING A DTD • An internal subset is declarations placed in the same file as the document content. • An external subset is located in a separate file. New Perspectives on XML, 2nd Edition Tutorial 3

  10. DECLARING A DTD • A DOCTYPE declaration can indicate both an external and an internal subset. The syntax is: <!DOCTYPE root SYSTEM “URI” [ declarations ]> or <!DOCTYPE root PUBLIC “id” “URL” [ declarations ]> New Perspectives on XML, 2nd Edition Tutorial 3

  11. DECLARING A DTD • The DOCTYPE declaration for an internal subset is: <!DOCTYPE root [ declarations ]> • Where root is the name of the document’s root element, and declarations are the statements that comprise the DTD. Placed in the same file as the document content New Perspectives on XML, 2nd Edition Tutorial 3

  12. DECLARING A DTD • The DOCTYPE declaration for external subsets can take two forms: • SYSTEM location <!DOCTYPE root SYSTEM “uri”> • root = document’s root element, • uri = location and filename of the external subset. Placed in an external file that is accessed from the XML document New Perspectives on XML, 2nd Edition Tutorial 3

  13. DECLARING A DTD • PUBLIC location. <!DOCTYPE root PUBLIC “id” “uri”> • root = document’s root element, • id = public identifier (a unique name that can be recognized by the parser . The public identifier acts as like a name space. ) • uri = location and filename of the external subset. • Use the PUBLIC location form when the DTD is placed in several locations or the DID is built into the XML parser itself. • Unless your application requires a public identifier, you should use the SYSTEM location form. New Perspectives on XML, 2nd Edition Tutorial 3

  14. DECLARING A DTD • If you place the DTD within the document, it is easier to compare the DTD to the document’s content. • However, the real power of XML comes from an external DTD that can be shared among many documents written by different authors. New Perspectives on XML, 2nd Edition Tutorial 3

  15. DECLARING A DTD • If a document contains both an internal and an external subset, the internal subset takes precedence over the external subset if there is a conflict between the two. • This way, the external subset would define basic rules for all the documents, and the internal subset would define those rules specific to each document. New Perspectives on XML, 2nd Edition Tutorial 3

  16. COMBINING AN EXTERNAL AND INTERNAL DTD SUBSET This figure shows how to combine an external and an internal DTD subset New Perspectives on XML, 2nd Edition Tutorial 3

  17. WRITING THE DOCUMENT TYPE DECLARATION This figure shows how to insert an internal DTD subset New Perspectives on XML, 2nd Edition Tutorial 3

  18. DECLARING DOCUMENT ELEMENTS • Every element used in the document must be declared in the DTD for the document to be valid. • An element type declaration specifies the name of the element and indicates what kind of content the element can contain. New Perspectives on XML, 2nd Edition Tutorial 3

  19. DECLARING DOCUMENT ELEMENTS • The element declaration syntax is: <!ELEMENT element content-model> element = element name (case sensitive) content-model = type of content the element contains. Note that DTD is not an XML language New Perspectives on XML, 2nd Edition Tutorial 3

  20. DECLARING DOCUMENT ELEMENTS • DTDs define five different types of element content: • Any elements. No restrictions on the element’s content. • Empty elements. The element cannot store any content. • #PCDATA. The element can only contain parsed character data. • Elements. The element can only contain child elements. • Mixed. The element contains both a text string and child elements. • Examples follow… New Perspectives on XML, 2nd Edition Tutorial 3

  21. TYPES OF ELEMENT CONTENT • ANY content: The declared element can store any type of content. The syntax is: <!ELEMENT element ANY> For example: <!ELEMENT products ANY> Is satisfied by any of the following: <products>SLR 100 digital Comera </products> <products /> <products> <name>SLR100 </name> <type> Digital CAMera </type> </products> New Perspectives on XML, 2nd Edition Tutorial 3

  22. TYPES OF ELEMENT CONTENT • EMPTY content: This is reserved for elements that store no content. The syntax is: <!ELEMENT element EMPTY> For example: <!ELEMENT img EMPLY> Is satisfied by following: <img /> New Perspectives on XML, 2nd Edition Tutorial 3

  23. TYPES OF ELEMENT CONTENT • Parsed Character Data content: These elements can only contain parsed character data. The syntax is: <!ELEMENT element (#PCDATA) • The keyword #PCDATA stands for “parsed-character data” and is any well-formed text string. For example: <!ELEMENT name (#PCDATA> Is satisfied by the following: <name> Lea Ziegler <name> New Perspectives on XML, 2nd Edition Tutorial 3

  24. TYPES OF ELEMENT CONTENT • ELEMENT content.: The syntax for declaring that elements contain only child elements is: <!ELEMENT element (children)> • Where children is a list of child elements. • For example: <!ELEMENT customer (phone)> is NOT satisfied by the following: <customer> <name>Lea Ziegler</name> <phone>555-2819</phone> </customer> New Perspectives on XML, 2nd Edition Tutorial 3

  25. TYPES OF ELEMENT CONTENT • The declaration <!ELEMENT customer (phone)> indicates the customer element can only have one child, named phone. You cannot repeat the same child element more than once with this declaration. New Perspectives on XML, 2nd Edition Tutorial 3

  26. ELEMENT SEQUENCES AND CHOICES • A sequence is a list of elements that follow a defined order. The syntax is: <!ELEMENT element (child1, child2, …)> • The order of the child elements must match the order defined in the element declaration. A sequence can be applied to the same child element. New Perspectives on XML, 2nd Edition Tutorial 3

  27. ELEMENT SEQUENCES AND CHOICES • Thus, <!ELEMENT customer (name, phone, email)> • indicates the customer element should contain three child elements for each customer. New Perspectives on XML, 2nd Edition Tutorial 3

  28. ELEMENT SEQUENCES AND CHOICES • Choice is the other way to list child elements and presents a set of possible child elements. The syntax is: <!ELEMENT element (child1 | child2 | …)> • where child1, child2, etc. are the possible child elements of the parent element. New Perspectives on XML, 2nd Edition Tutorial 3

  29. ELEMENT SEQUENCES AND CHOICES • For example, <!ELEMENT customer (name | company)> • This allows the customer element to contain either the name element or the company element. However, you cannot have both the customer and the name child elements since the choice model allows only one of the child elements. New Perspectives on XML, 2nd Edition Tutorial 3

  30. MODIFYING SYMBOLS • Modifying symbolsare symbols appended to the content model to indicate the number of occurrences of each element. There are three modifying symbols: • a question mark (?), allow zero or one of the item. • a plus sign (+), allow one or more of the item. • an asterisk (*), allow zero or more of the item. New Perspectives on XML, 2nd Edition Tutorial 3

  31. MODIFYING SYMBOLS • For example, <!ELEMENT customers (customer+)> would allow the document to contain one or more customer elements to be placed within the customers element. • Modifying symbols can be applied within sequences or choices. They can also modify entire element sequences or choices by placing the character immediately following the closing parenthesis of the sequence or choice. New Perspectives on XML, 2nd Edition Tutorial 3

  32. MIXED CONTENT • Mixed content elements contain both character data and child elements. The syntax is: <!ELEMENT element (#PCDATA | child1 | child2 | …)*> • This form applies the * modifying symbol to a choice of character data or elements. Therefore, the parent element can contain character data or any number of the specified child elements, or it can contain no content at all. New Perspectives on XML, 2nd Edition Tutorial 3

  33. MIXED CONTENT • Because you cannot constrain the order in which the child elements appear or control the number of occurrences for each element, it is better not to work with mixed content if you want a tightly structured document. New Perspectives on XML, 2nd Edition Tutorial 3

  34. DECLARING ELEMENT ATTRIBUTES • For a document to be valid, all the attributes associated with elements must also be declared. To enforce attribution properties, you must add an attribute-list declaration to the document’s DTD. New Perspectives on XML, 2nd Edition Tutorial 3

  35. ELEMENT ATTRIBUTES IN KRISTEN’S DOCUMENT This figure shows element attributes in Kristen's document New Perspectives on XML, 2nd Edition Tutorial 3

  36. DECLARING ELEMENT ATTRIBUTES • The attribute-list declaration : • Lists the names of all attributes associated with a specific element • Specifies the data type of the attribute • Indicates whether the attribute is required or optional • Provides a default value for the attribute, if necessary New Perspectives on XML, 2nd Edition Tutorial 3

  37. DECLARING ELEMENT ATTRIBUTES • The syntax to declare a list of attributes is: <!ATTLIST element attribute1 type1 default1 attribute2 type2 default2 attribute3 type3 default3…> element = name of the element associated with the attributes attribute = name of an attribute type = attribute’s data type default = whether the attribute is required or implied, and whether it has a fixed or default value. New Perspectives on XML, 2nd Edition Tutorial 3

  38. DECLARING ELEMENT ATTRIBUTES • Attribute-list declaration can be placed anywhere within the document type declaration, although it is easier if they are located adjacent to the declaration for the element with which they are associated. New Perspectives on XML, 2nd Edition Tutorial 3

  39. WORKING WITH ATTRIBUTE TYPES • While all attribute types are text strings, you can control the type of text used with the attribute. There are three general categories of attribute values: • CDATA • enumerated • Tokenized • CDATA types are the simplest form and can contain any character except those reserved by XML. • Enumerated types are attributes that are limited to a set of possible values. New Perspectives on XML, 2nd Edition Tutorial 3

  40. CDATA format: <!ATTLIST element attribute CDATA default> Example: <!ATTLIST item itemPrice CDATA …> Permits the following in the XML document <item itemprice=“29.95”> … <item> New Perspectives on XML, 2nd Edition Tutorial 3

  41. WORKING WITH ATTRIBUTE TYPES • Enumerated types are attributes that are limited to a set of possible values: attribute (value1 | value2 | value3 | …) • For example: customer custType (home | business )> • restrictsCustType to either “home” or “business” New Perspectives on XML, 2nd Edition Tutorial 3

  42. WORKING WITH ATTRIBUTE TYPES • notation (another kind of enumerated attribute) • It associates the value of the attribute with a <!NOTATION> declaration located elsewhere in the DTD. • The notation provides information to the XML parser about how to handle non-XML data. • More about this later New Perspectives on XML, 2nd Edition Tutorial 3

  43. WORKING WITH ATTRIBUTE TYPES • Tokenized types = text strings that follow certain rules for the format and content. The syntax is: attribute token • There are seven tokenized types. • The ID token is used with attributes that require unique values. For example, if a customer ID needs to be unique, you may use the ID token: customer custID ID • This ensures each customer will have a unique ID: <customer custID=“Cust021”> … </customer> <customer custID=“Cust022”> … </customer> New Perspectives on XML, 2nd Edition Tutorial 3

  44. WORKING WITH ATTRIBUTE TYPES • IDREF token must have a value equal to the value of an Id attribute located somewhere in the same document • Like a “foreign key” in relational databases • General format; <!ATTLIST element attribute IDREF default> • Example <!ATTIST customer forCustomer IDREF …> • The document must contain an customer element whose ID value matches the value of forCustomer For example <customer ID=“OR3413”> … <customer> <order forCustomer = “OR3413”> … </order> New Perspectives on XML, 2nd Edition Tutorial 3

  45. WORKING WITH ATTRIBUTE TYPES • NMTOKEN (name token) is used with character data whose value must be valid XML names • More about this later… New Perspectives on XML, 2nd Edition Tutorial 3

  46. ATTRIBUTE TYPES This figure shows the attribute types New Perspectives on XML, 2nd Edition Tutorial 3

  47. ATTRIBUTE DEFAULTS • Default has four possible defaults: • #REQUIRED: the attribute must appear with every occurrence of the element. <!ATTLIST customer custID ID #REQUIRED> • #IMPLIED: The attribute is optional. <!ATTLIST customer custID ID #IMPLIED> • An optional default value: A validated XML parser will supply the default value if one is not specified <!ATTLIST item quantity CDATA “1”> • #FIXED: The attribute is optional but if one is specified, it must match the default. <!ATTLIST customer rating CDATA “1” #FIXED> “Red” indicates correction “Red” indicates correction New Perspectives on XML, 2nd Edition Tutorial 3

  48. INSERTING ATTRIBUTE-LIST DECLARATIONS This figure the revised contents of the Orders.xml file attribute declaration New Perspectives on XML, 2nd Edition Tutorial 3

  49. WORKING WITH ENTITIES • General entity = entity that references content to be used within an XML document. An entity be refer to: • a text string • a DTD • an element or attribute declaration • an external file containing character or binary data • Parsed entity = referenes text that can be interpreted or parsed • Unparsed entity = references content that can not be parsed, e.g., graphic image I use an “entity” like a “macro” from some programming languages. New Perspectives on XML, 2nd Edition Tutorial 3

  50. Introducing Entities • Built in entities: • &amp; for the & character • &lt; for the < character • &gt; for the > character • &apos; for the ‘ character • &quot; for the ” charcter New Perspectives on XML, 2nd Edition Tutorial 3

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