CSC/ECE 517 Fall 2009/wiki3 4 dt

Introduction

The DRY (Don’t Repeat Yourself) principle states that every piece of knowledge must have a single, unambiguous, authoritative representation within a system. It is a software engineering principle for efficient software development, build, test, deployment and documentation. It can be applied to all the levels in the software development life cycle. It was formulated by Andy Hunt and Dave Thomas with an intention that a change in the data / code in a single element should not affect other unrelated elements. There are advantages of following this principle in software like ease of maintenance, good understanding of the code etc. DRY principle is not only confined to coding methodologies but is much broader and is extended to any duplication of data. This article throws some light upon various instances where data is duplicated in the real world. Each scenario is described with pros and cons.

Examples of DRY principal on data

Database

In case of a database it is desirable to have a single copy of data. A database, specially the one that satisfies the third normal form, has the feature that a single piece of information is stored only once. This leads to efficient use of memory as less memory would be required for storing data. It becomes easier to maintain and update because changes need to be made only in one place. This also makes the database less prone to errors because if there were multiple copies of this data then it is quite possible that they do not match. But if only one copy is present then there is no question of mismatch of data.