Page 261 -

228 Part 3 • the analysis Process

Figure 8.17
A document type definition
for the customer XML
document. < !DOCTYPE customers [
< !ELEMENT customers
< !ELEMENT customer
(customer) + >
< !ATTLIST customer number
< !ELEMENT name (name, address, current_balance, order*) >
ID #REQUIRED>
< !ATTLIST name type
< !ELEMENT lastname (lastname, firstname, middle_initial?) >
(I  C) #REQUIRED>
< !ELEMENT firstname
(#PCDATA) >
(#PCDATA) >
< !ELEMENT middle_initial
< !ELEMENT address
(#PCDATA) >
< !ELEMENT street
< !ELEMENT apartment (street, apartment?, city, state, zip, country) >
(#PCDATA) >
< !ELEMENT city
(#PCDATA) >
< !ELEMENT state
(#PCDATA) >
< !ELEMENT zip
(#PCDATA) >
< !ELEMENT country
(#PCDATA) >
(#PCDATA) >
< !ELEMENT current_balance
< !ELEMENT order
(#PCDATA) >
< !ATTLIST order customer_number
< !ELEMENT order_number (order_number, order_date, ship_date, total) >
IDREF #REQUIRED>
< !ELEMENT order_date
(#PCDATA) >
(#PCDATA) >
< !ATTLIST order_date format
< !ELEMENT payment
< !ELEMENT check (mmddyyyy  yyyymmdd  ddmmyyyy) #REQUIRED>
(check  credit_card) >
< !ELEMENT credit_card
(check_number) >
< !ATTLIST credit_card type
(credit_card_number, expiration_date) >
< !ELEMENT credit_card_number
(M  V  A  D  O) #REQUIRED>
(#PCDATA) >
< !ELEMENT expiration_date
< !ELEMENT payment_date
(#PCDATA) >
(#PCDATA) >
< !ATTLIST payment_date format
< !ELEMENT payment_amt
] > (mmddyyyy  yyyymmdd  ddmmyyyy) #REQUIRED>
(#PCDATA) >
be present in an ID somewhere in the document. An attribute list containing values in paren-
theses means that the attribute must contain one of the values. A DTD definition <!ATTLIST
credit_card type (M|V|A|D|O) #REQUIRED> means that the credit card type must be either an
M, V, A, D, or O.
XML Schemas
A schema is another, more precise way to define the content of an XML document. Schemas
may include the exact number of times an element may occur as well as the type of data within
elements, such as character or numeric values, including the length of the element, limits on the
data, and the number of places to the left and right of a decimal number.
A data dictionary is an excellent starting point for developing an XML document and a
document type of definition or schema. The advantage of using XML to define data is that, in
the XML format, data are stored in a pure text format and not dependent on any proprietary
software. The document may be easily validated and transformed into many different output
formats.
Industry groups or organizations may be involved in defining an industry-specific XML
structure so that all involved parties understand what the data mean. This is very important when
an element name may have several meanings. An example is “state,” which may mean a postal
state abbreviation or the state of an order or account. Examples of industry-specific XML docu-
ment type definitions and schemas may be found at www.xml.org.