<ch59 toc ch61>

# 60
Structured English

60.1 Purpose
60.2 Strengths, weaknesses, and limitations
60.3 Inputs and related ideas
60.4 Concepts
60.4.1 Sequence
60.4.2 Blocks of logic
60.4.3 Decision or selection
60.4.4 Repetition or iteration
60.5 Key terms
60.6 Software
60.7 References

60.1 Purpose

Structured English is a very limited, highly restricted subset of the English language used to plan, design, or document program routines, modules, and manual procedures.

60.2 Strengths, weaknesses, and limitations

Structured English is useful for planning or designing program routines, modules, and manual procedures. It resembles a programming language, so programmers find it easy to understand. The base for structured English is, of course, English, so users find it easy to follow, too.

Structured English is excellent for describing an algorithm, particularly when user communication is essential. If the main concern is communication with the programmers, however, pseudocode may be a better choice. Structured English is not a good choice for describing a high-level control structure or an algorithm in which numerous decisions must be made; logic flowcharts, decision tables, and decision trees are better for such tasks.

60.3 Inputs and related ideas

Before writing structured English, the designer must understand the algorithm or procedure. The necessary information might be compiled from direct observation, extracted from existing documentation, or derived from the problem definition (Part II) and/or analysis (Part IV) stages of the system development life cycle.

Other tools for documenting or planning routines or processes include logic flowcharts (# 55), Nassi-Schneiderman charts (# 56), decision trees (# 57), decision tables (# 58), pseudocode (# 59), and input/process/output (IPO) charts (# 64). A pseudocode routine usually exists in the context of a larger program. Tools for documenting or planning program structure include structure charts (# 63) and HIPO (# 64). The basic software logic blocks are defined in # 62.

60.4 Concepts

There are several variations of structured English, none of which can be considered a standard. Consequently, view this # as a guideline.

A good structured English statement reads like a short imperative sentence. By convention, only key words such as IF, THEN, SO, REPEAT, UNTIL, DO, and so on are capitalized; data names and the general English needed to complete a sentence or a phrase are lower case. Many sources recommend that a data name defined in a data dictionary be underlined, and that convention will be followed in the examples shown below.

60.4.1 Sequence

Sequence statements begin with commands such as MOVE, GET, WRITE, READ, or COMPUTE followed by the name or names of the associated data elements or data structures. For example,

COMPUTE gross pay.
ADD 1 to counter.
MULTIPLY hours worked by pay rate to get gross pay.
GET inventory record.
MOVE customer name to invoice.
WRITE invoice.

60.4.2 Blocks of logic

It is often convenient to group several structured English statements into a block, assign a name to the block, and reference the block by coding a single sequence statement. For example, all the instructions required to compute gross pay might be grouped in a block under the name compute gross pay. Subsequently, the statement

DO compute gross pay.

references the entire block.

Note that a block can contain any combination of code, including decisions, repetitive logic, and even other blocks. Indentation should always be used to show the relationship between the parts of a block.

60.4.3 Decision or selection

Decision (or selection) logic follows an IF-THEN-ELSE structure:

IF condition
THEN block-1
ELSE (not condition)
SO block-2.

The key word IF is followed by a condition. If the condition is true, the block following THEN is executed. ELSE identifies the negative of the condition. SO precedes the block to be executed if the initial condition is false. For example,

IF stock-on-hand is less than reorder-point
THEN turn on reorder-flag
ELSE (stock-on-hand not less than reorder-point
SO turn off reorder-flag.

Indenting makes the IF-THEN-ELSE logic easier to read. (Note: The negative condition following ELSE is often assumed and not explicitly coded.)

Nested decisions are also supported:

IF condition-1
THEN IF condition-2
THEN block-a
ELSE (not condition-2)
SO block-b
ELSE (not condition-1)
SO block-c.

Note that any or all of block-a, block-b, or block-c could contain yet another decision.

60.4.4 Repetition or iteration

Repetitive (or iterative) logic defines a block of structured English that is executed repetitively until a terminal condition is reached. For example, such instructions as:

REPEAT UNTIL condition-1



imply both repetitive logic and the condition used to terminate that logic.

60.5 Key terms

Module —
A portion of a larger program that performs a specific task.
Procedure —
A set of guidelines, rules, and instructions for performing a task; often, a manual procedure.
Routine —
A set of instructions that performs a specific, limited task.
Structured English —
A very limited, highly restricted subset of the English language used to plan, design, or document program routines, modules, and manual procedures.

60.6 Software

Few software tools are designed to produce structured English. Word processors and text editors are sometimes used.

60.7 References

1.  Davis, W. S., Systems Analysis and Design: A Structured Approach, Addison-Wesley, Reading, MA, 1983.
2.  Gane, C. and Sarson, T., Structured Systems Analysis: Tools and Techniques, Prentice-Hall, Englewood Cliffs, NJ, 1979.
<ch59 toc ch61>