Common Mechanisms of UML

Transaction Flow

What is Transaction flow?

Ø  A unit of work seen from a system users point of view is known as transaction

Ø  It contains the sequence of operations, some of which are performed by a system, persons or devices that are outside of the system

Ø  Transactions begin with birth, i.e. they are created as a result of some external act

Ø  At the conclusion of the transactions processing, the transaction is no longer in the system

Example:
Following are the steps included in a transaction for an online information retrieval system

v  Accept input(tentative birth)

v  Validate input(birth)

v  Transmit acknowledgment to requester

v  Do input processing

v  Search file

v  Request directions from user

v  Accept input

v  Validate input

v  Process request

v  Update File

v  Transmit output

v  Record transaction in log and clean up(death)

Usage:

v  Online systems are most complicated system. In this, the transaction flows are indispensable for specifying requirements.

v  Air traffic control or airline reservation systems are the big systems. It has thousands of different transaction flows

v  The flows are represented by relatively simple flow graphs, many of which have a single straight-through path

v  Loops are infrequent compared to control flow graphs

v  The most common loop is used to request a retry after 'user input' errors

Example: An ATM system allows the user to try, say three times, and will take the card away the fourth time.

Implementation:

v  The implementation of a transaction flow is generally implicit in the systems control structure and the database it uses

v  A transaction flow is a representation of a path taken by a transaction through a succession of processing modules. Think of each transaction as represented by a token that passes from one routine to routine as it progresses through flow

v  Transaction flow graph is a diagrammatic representation of what happens to the tokens

v  These tokens are, in general not manipulated by the control structure of the program

Perspective:

v  Transaction flow testing is the ultimate black box testing as all we know is that there is a transaction and the system will do predictable actions to the transaction

v  Transaction flow graphs are kind of data flow graphs as we look at the various data objects and the operation performed on them

v  We should note that the decision nodes of transaction flow graph can be complicated in their own rights

v  Our transaction flow model should be a simplified version of those decisions