Web Applications with Javascript or Java by Gerd Wagner

Author:Gerd Wagner
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2018-04-13T04:00:00+00:00

Part IIConstraint Validation

For catching various cases of flawed data, we need to define suitable integrity constraints that can be used by the application’s data validation mechanisms. Integrity constraints may take many different forms. The most important type of integrity constraints are property constraints, which define conditions on the admissible property values of an object.

7Integrity Constraints and Data Validation

7.1Introduction

For detecting non-admissible and inconsistent data and for preventing such data to be added to an application’s database, we need to define suitable integrity constraints that can be used by the application’s data validation mechanisms for catching these cases of flawed data. Integrity constraints are logical conditions that must be satisfied by the data entered by a user and stored in the application’s database.

For instance, if an application is managing data about persons including their birth dates and their death dates, then we must make sure that for any person record with a death date, this date is not before that person’s birth date.

Since integrity maintenance is fundamental in database management,the data definition language part of the relational database language SQL supports the definition of integrity constraints in various forms. On the other hand, however, there is hardly any support for integrity constraints and data validation in common programming languages such as PHP, Java, C# or JavaScript. It is therefore important to take a systematic approach to constraint validation in web application engineering, like choosing an application development framework that provides sufficient support for it.

Unfortunately, many web application development frameworks do not provide sufficient support for defining integrity constraints and performing data validation. Integrity constraints should be defined in one (central) place in an app, and then be used for configuring the user interface and for validating data in different parts of the app, such as in the user interface and in the database. In terms of usability, the goals should be:

To prevent the user from entering invalid data in the user interface (UI) by limiting the input options, if possible.

To detect and reject invalid user input as early as possible by performing constraint validation in the UI for those UI widgets where invalid user input cannot be prevented by limiting the input options.

To prevent that invalid data pollutes the app’s main memory state and persistent database state by performing constraint validation also in the model layer and in the database.

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