2. How many times can an element occur? How many times must an element occur? Cardinality
3. A student must have a first name A student may or may not have a last name A student may have one or more majors, or none (undeclared) <!ELEMENT student (first, last?, major*)> Note: Cardinality indicator doesn’t affect the element declaration (i.e. major) Cardinality: Example
4. Elements tend to be used to describe a logical unit of information Attributes are typically used to store data about characteristics (properties) May have a Movie element with attributes for Title, Rental Price, Rental Days No specific rules about how to use elements and attributes Attributes and DTD’s
5. Attributes allow more limits on data Can have a list of acceptable values Can have a default value Some ability to specify a data type Concise, about a single name/value pair Attributes have limits Can’t store long strings of text Can’t nest values Whitespace can’t be ignored Attributes and Elements
6. Declaration: <!ATTLISTElementNameAttrNameAttrType Default> Specify the Element the attribute belongs to Specify the Name of the attribute Specify the Type of data the attribute stores Specify characteristics of the values (Default or attribute value) List either the default value or other characteristic of value – required, optional Specifying Attributes
7. CDATA – unparsed character data Enumerated – series/list of string values Entity/Entities – reference entity definition(s) ID – unique identifier for the element IDREF – refer to the ID of another element IDREFS – list of ID’s of other elements separated by whitespace NMTOKEN/NMTOKENS – value(s) of attribute can be anything that follows rules for XML name Sample Attribute Data Types
8. Specifies that attribute value must be found in a particular list Each value in list must be valid XML name Limits on spaces, characters Use | (pipe) to separate members of list If specifying list letter grades for a student: <!ATTLIST student grade (A | B | C | D | F | V | W | I) #IMPLIED> Enumerated Attributes Element Attribute Enumerated List
9. An ID specifies that the element must have a unique value within the document Allows reliable way to refer to a specific element No spaces allowed in value Typically replace space with underscore Attribute list can include only one ID IDREF, IDREFS allows an element to be associated with another or multiple other elements A student element must have a student ID: <!ATTLIST student studentID ID #REQUIRED> ID, IDREF, IDREFS
10. Attributes can refer to entities “Entity” refers to substituting a reference for a text value & refers to the & character Unparsed Entity is a reference that isn’t parsed Can reuse references for long values, or hard to manage characters (i.e. tab, line feed) Entity must be declared in the DTD <!ENTITY classTitle “XML”> When classTitle found in document, replaced with XML Entities and Attributes
11. Can specify how the value will appear in the document Must always specify a value declaration DEFAULT sets a value for an attribute if a value isn’t provided Include default value in double quotes FIXED sets a value that must occur; if an attribute has a different value, a validation error occurs REQUIRED specifies that the attribute (and value) must exist IMPLIED means the attribute is optional Attribute Value Declarations
