Mastering Web Site Development/Microsoft Mastering Web Site Development (Microsoft) (1997).iso/Media/Ch09/W09A010.cc2

Text File | 1997-04-24 | 2.9 KB | 53 lines

0, In this animation, you will learn how transactions
6, and ActiveX server components are processed by
8, Microsoft Transaction Server. In this scenario, a
13, user enters a request from a Web page to transfer
16, $100 from a checking account to a savings account.
21, When the request is received, an Activer Server Page
24, runs and creates a transfer object to transfer the
28, money. You write the transfer object, which is an
31, ActiveX server component. When the transfer object
35, is called, Microsoft Transaction Server
39, automatically creates a Context object. Whenever an object
45, is created in Microsoft Transaction Server an
48, associated Context object is also created. The
53, Context object manages the context for the object. The
58, transfer object requires a transaction and the
62, Context object creates the transaction. The context of
68, a transaction is shared across all objects
71, involved in the transaction. And, the context ends when
75, the transfer object is finished running. Any work
79, done inside the transaction is buffered until all
83, objects commit or an object aborts. The transfer
89, object requires and creates two additional objects
93, to complete its work: debit, and credit. These
97, objects are also ActiveX server components. When a
101, transaction exists, the context of the transaction
105, extends to include the credit object in the
108, existing transaction. In this scenario, the credit object adds
112, $100 to the savings account. When the change is
117, finished, the credit object indicates that it has
120, completed its task successfully in the context of the
123, transaction. The transfer object then creates the
128, debit object, which is also incorporated in the
131, existing transaction. The debit object subtracts
135, $100 from the checking account. When the change is
138, finished the debit object also indicates that it
142, has completed its task successfully in the context
145, of the transaction. Finally, the transfer object
149, indicates that it has completed its work. All
153, objects in the transaction have completed successfully,
157, so the transaction can commit and the database
159, changes are permanent. If any object in the
163, transaction fails to complete its work successfully, the
167, transaction aborts. For example, even though the
171, credit object may succeed, the debit object may
174, fail because the checking account has a zero balance. Money
178, cannot be taken from an empty account so the debit
181, object indicates that it has to abort. Once all
187, objects have finished running, the transaction rolls
190, back to undo the changes made by the credit
192, object. Because the debit object has aborted, the
196, credit object cannot commit and the integrity of the
199, database is protected.
202, END