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.
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: