Writing Effective Natural Language Requirements Specifications

Information should never be arbitrarily grouped together—it makes the document difficult to understand and to maintain. Descriptions of the conditions
and situations that the required capability will encounter must be located with
the prescription of its required response; however, the description and prescription must be kept distinct from one another. Requirements that are parts of a single functional capability must be grouped together, e.g., functions that are connected in series by output-to-input relationships should appear in the SRS in the same sequence, if possible.

Functions that share common inputs and outputs should be addressed within the same section of the SRS. If several processes must be accomplished in the same time frame, their specifications must be tied together by the document’s structure to make this commonality clear. Similar functions need to be distinguished from one another but the similarities also need to be emphasized. Most of these restrictions can be satisfied by combining a requirements identification scheme that consistently uses similar numbers to number similar things and by using a writing style that uses short declarative sentences.