Warnier-Orr notation is one tool that helps analysts and programmers make systems and programs that are Correct.  Structured Pseudocode is another tool that we'll look at later.  I like Warnier's notation best and find that it helps new programmers to develop a well-structured mental model required for work in information systems. 

Simple Lists of Output Requirements, Data & Actions, and Input can help get us started thinking about what is required in a solution.  Lists, when indented, can only show a simple sequence & hierarchy of data & action requirements. 

But lists are limited in describing System Architecture.  Computer Systems use logical structures that select alternative Actions depending on the value of the data that are being processed.  And, computer algorithms do a lot of repetitive Actions.   

A notation for structured design of systems & programs needs to handle: Sequences, Alternative Selection, and Repetition.  

Warnier's notation, as adapted into the B-Liner program, uses bullets, brackets, some parentheses, and the 'exclusive or' symbol to clearly show sequences, alternative selections, and loops that are components of well structured algorithms.

To introduce Warnier-Orr diagrams, here is the simple Payroll System above, using Warnier's notation to show a structured view of the set of Actions from our black box.  It shows what the system needs to do each day, month, and year to generate the required output keep the records accurate.  It does not show any detail for the algorithms needed in the scripts, but we'll leave these out for the time being.

This is a 'high level' system diagram that shows none of the Details about the sequences, alternative selections, and loops that go into the system's scripts.  

But, it demonstrates how the system is hierarchically organized and how each function is related logically either by sequence, alternative selection, or repetition.

One of the strengths of Warnier's notation is that it can be used for both high level design and for detailed program design.  We'll look more at the detailed program design in class.

Many business processes are calendar-driven, so the systems that handle the processes need to be, too.  So, following one-time startup activity of this payroll system, the cycles of the system are continuous, controlled by years, months, and days.

The First bullet at the left represents the entire set of Actions of the system.  This small system is 'broken down into' two parts: Startup activity & Annual Operations, each of these shown with it's own bullet.  

When a Payroll System starts up, before it can produce the first pay check, its 'code tables' need to be loaded to describe everything about the system: earning codes, pay cycles, deductions, what pension & insurance plans, &c, &c about the company are defined.  Employee records need to be entered into the system, or 'taken on' from a previous system.

Payroll processing has an Annual cycle: at the beginning of each year, before January 31, the IRS requires W-2 forms reporting payroll data for the prior year to be provided for itself & for each employee. And a W-3 form that accompanies the W-2's is also sent to the IRS.  So, at the beginning of each calendar year, a Payroll Office is busy getting these forms prepared.  A payroll system needs to be sensitive to the Calendar Year (YYYY) and repeat its annual cycles for each year that it operates.

The (YYYY) under the line Annual Operations means that the actions in this bracket are repeated for each year: 1999, 2000, 2001, & so on until the system is abandoned.  This is how Warnier's notation shows Loops.  In the logical construction of systems these 'controlling variables' are quite important.

At the end of each year, tax tables are likely to change so Year End activity includes finding & entered all the applicable tax tables into the system so that the system will be compliant with Payroll Regulations.

The next Cycle of operation within Yearly is Monthly.  Some activity begins each month: Preparation of Quarterly reports is needed for the end of each quarter; Monthly reports for each month are prepared in the first few days of the following month.

Within each Monthly cycle of operation, there are Daily operations:  The system's users need to be able to make additions and changes to the 'code tables' and employees' records.  As changes occur in the Real World the computer records are maintained to reflect the changes.  Managers & employees will call with 'ad hoc' requests for information stored in the system.  YYYYMMDD, in this diagram, refers to the Calendar Date:  20020101 is January 1, 2002; 20021231 is December 31, 2002

Weekly Cycles have a routine where Payroll Worksheets are printed, and Timesheet data are entered, then a Payroll Edit Report is printed so that errors can be easily detected before Checks are run.  If there are Edit Errors (a logical test), then the system's Users need to find the errors and correct them.  After any errors are corrected it is time to Print Checks for: the Employees, the Bank that receives the Federal withholdings, deductions, and payroll taxes; the State; the Insurance company; the Pension Plans; and anybody else that gets paid, like the Court when an employee's wages are garnished.

Here are the key points of Warnier's notation:

Each statement in a Warnier diagram is either an Action or a Logical Condition.  They are structured into Sequences, Alternative Selections, and Loops.

An Action, like Maintain Codes, may have a bracket placed to its right that contains a more detailed logical sequence that more completely shows how the action is performed.  

Unless an Alternative Selection or a Loop alters the flow of Actions, one Action follows another in Sequence.  A sequence of actions may be listed under one bullet.    

Alternatives in an alternative selection each have a bullet of their own, & they have a bracket to their right which contains the Actions that will result if the Condition evaluates as True.  If there is more than one Alternative (if/then/else or case), each is separated from the prior using an 'exclusive OR' symbol.

Loops also have a bullet and bracket of their own, and are shown using a repetition indicator in parenthesis (Like YYYY) under the bulleted Statement that defines or controls the Loop.  Whatever style is adapted, the bulleted statement and statements in the bracket should show clearly the type of loop (while, until, for/next) and what controls it.

Later pages and classroom demonstrations will address how Warnier's notation is applied to program design. 

How is Structure implemented in PowerBuilder?  This next page shows the logical Structures as they appear in PowerScript...