• Chapter 1: Getting Started with Stylus Studio
• Chapter 2: Editing and Querying XML
• Chapter 3: Converting Non-XML Files to XML
• Chapter 4: Working with XSLT
• Chapter 5: Creating XSLT Using the XSLT Mapper
• Chapter 6: Debugging Stylesheets
• Chapter 7: Defining XML Schemas
• Chapter 8: Defining Document Type Definitions
  • What Is a DTD?
  • Creating DTDs
  • About Editing DTDs
  • About Modifiers in Element Definitions in DTDs
  • Defining Elements in DTDs
  • Defining General Entities and Parameter Entities in DTDs
    • Steps for Defining Entities in DTDs
    • General Entity Example in a DTD
    • Parameter Entity Example in a DTD
  • Inserting White Space in DTDs
  • Adding Comments to DTDs
  • About Node Properties in DTDs
  • Associating an XML Document with an External DTD
  • Moving an Internal DTD to an External File
• Chapter 9: Writing XPath Expressions
• Chapter 10: Working with XQuery in Stylus Studio
• Chapter 11: Composing Web Service Calls
• Chapter 12: Accessing Relational Data as XML
• Chapter 13: Extending Stylus Studio
• Chapter 14: Stylus Studio GUI Reference

Home > Online Product Documentation > Table of Contents > Defining General Entities and Parameter Entities in DTDs

Defining General Entities and Parameter Entities in DTDs

In DTDs, an entity allows you to define a symbol for a value. In the Tree view, you can define general entities and parameter entities. The value of a general entity can be just about anything. It can be

General entities are useful for things that change often, such as the name of a product in development. An entity allows you to change the value in one place and have the corrected value appear everywhere it is needed.

See also Description of Entity and Parameter Entity Properties in DTDs.

When you define a general entity, you specify a symbol that you can use in instance documents. When the XML parser finds a reference to a general entity, it replaces the symbol with the value you specified when you defined the general entity.

When you define a parameter entity, you specify a symbol that you can use elsewhere in the DTD. Again, when the XML parser finds a reference to a parameter entity, it replaces the reference with the value you specified when you defined the parameter entity.

In a DTD, the definition of an entity must appear before a reference to that entity. Therefore, it is good practice to put all entity declarations at the beginning of a DTD.

This section discusses the following topics:

Steps for Defining Entities in DTDs

The procedures for defining general entities and parameter entities are almost the same.

To define an entity in the Tree tab:

2. In the left tool bar, click New Entity or New Parameter Entity .

If you want to define the value for this entity in this DTD, the value should be Internal. Otherwise, the value should be External. If you need to change the value of the Location property, double-click its current value. In the drop-down menu that appears, double-click the new value.

Although you can also specify a value for the Public ID property, Stylus Studio ignores any value you specify. A Public ID is a string that some parsers can resolve to an address, which they then use to locate a file. Stylus Studio does not have this capability.

General Entity Example in a DTD

Suppose you define the shopname general entity as an internal entity with the value Most Excellent Book Store of Tokyo. In the Text view of the DTD, this appears as follows:

<!ENTITY shopname "Most Excellent Book Store of Tokyo">
               

            

In an instance document, when the XML parser finds &shopname;, it replaces it with Most Excellent Book Store of Tokyo.

Parameter Entity Example in a DTD

Suppose you define the invoice parameter entity as an internal entity as follows:

<!ENTITY % customer "name, street, city, state, zipcode">
               

            

The percent sign ( %) after the ENTITY keyword indicates that this is a parameter entity. Later in the DTD, you can reference this parameter entity as follows:

<!ELEMENT invoice (%customer;, item, price, date)>
               

            

When this DTD is processed, it is as if you had specified the following:

<!ELEMENT invoice (name, street, city, state, zipcode, item, price, date)>