Trong trường hợp này, tất cả các hệ thống không gian Gems DMZ1 và DMZ2 có thể có phần mềm máy chủ Web được cài đặt trên chúng. Cũng có thể có phần mềm máy chủ Web được cài đặt trên một số hệ thống mạng riêng. Bây giờ, nếu một người dùng cuối một nơi nào đó trên Internet vào | 186 Chapter 5 Schema Document Structures There are almost as many ways to create a logical structure for a schema document as there are schema documents. But they are all variations or combinations of two basic approaches the nesting approach or the flat catalog approach. The Nesting Structure The nesting structure is based on a predominance of locally declared data types Figure uses element type declarations as examples . Figure illustrates the element type hierarchy of a nesting approach. A full element declaration is inserted every time an element type is needed. Notice that in Figure there are no ref elementxx declarations. Figure depicts the schema document that reflects the hierarchy presented in Figure . In the generic schema document depicted in Figure the element type named element6 appears within four other element types element2 element4 element5 and element7 . It is fully declared within each one and in each case the declaration is identical. Many programmers call this structure the nesting doll or Russian doll structure since the element declarations are cloaked one within another reminiscent of those festive hollow dolls that act as containers for identical but smaller dolls. Among the advantages to the nesting structure are the ease with which you can create context-sensitive element tags. However compared to the flat catalog discussed in the next section the XML parser uses more resources when processing this type of schema. Further if a designer wants to make changes to for example the element6 declaration in Figure then those changes must be made to the element6 declarations in all four locations. This takes time and may introduce the risk of mistakes in one or more of the element6 declarations. That may not be a big issue for a small schema but it could be problematic for larger schemas. xs schema I name element1 I---------------------1--------------------1 name element 2 name element 3 name element 4 name element 5 .
