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Specifying your requirements

Looking back over past database projects, the one factor which differentiates the successful from the not-so-successful is whether we were able to define the requirements accurately at the start. If you have a really clear idea of what you want your database to do then you are half way to a successful project.

The process of creating a requirements specification is usually a joint effort between the customer and the database developer, starting with the customer's view of the database. As the customer, you understand your business and what you need the database to do. Our job is to translate this information into a technical specification on which to base the design. It is rare at this stage to be able to define everything in complete detail, but it is important to be able to lay down the basics accurately. For example, it is very important to agree the data types and relationships early on - any change after the project has started may mean major rework of existing forms, code, queries and reports.


The business context

A business database is usually designed to model some part of the business process of the company using it. Ideally, a requirements specification should start with a brief description of the how the business operates, in particular the part of the business which the database will model. This section does not need to be long - a paragraph or two is usually enough - but it is important. It will provide a reality check at each stage of the design: "Will the database operate like the business? Will it add value to the process?" A database requires an investment of time and money. It is important to make sure it is paying back that investment with interest!

Scope

It may be tempting to put everything you can think of into a database, but recognise that you will get the best payback from areas where

  • Large quantities of data are involved
  • Data is changing, or new data is being generated continually
  • Up-to-date data needs to be shared between users
  • The data is central to the operation of the company

For example, if your company generates large numbers of quotations and invoices then they should almost certainly be on a database. But think twice about including major customer contracts. Even though this data is very important to the company, if you only handle half a dozen each year then putting them on a database is probably more trouble than it's worth - it would be easier to rely on a word-processor and spreadsheets.

User scenarios

Think who the potential users of the system will be and to describe how they will interact with the system.

  • What groups of users will use the system?
  • Will they need access to different areas of the system?
  • Do they need different levels of access into each part of the system (e.g. administration, manager, clerical, read-only)
  • What data will members of each group input into the system and where will it come from?
  • What information will each type of user need to extract from the system?
  • What types of reports will be needed by each type of user?

Data

List the types of data to be stored. The list may include such items as customer companies and contacts, quotations, advice notes, invoices, dispatches, supplier companies, supplier products, orders, order items, payments received, payments made, etc. In the database each type of data would be stored in a separate table.

Describe as much as you can about the relationships between the types of data. For example, there would usually be a "one-to-many" relationship between a company and the company contacts, or between an order and the order items.

For each table we will need to decide exactly what data "fields" are to be stored. For example, for each contact we may want to store obvious things such as last-name, first-name, title, position in company, and less obvious things such as whether they are a present employee of the company or a past employee. If these details are not known at the start it is less critical. They can be filled in later. What is critical is that the tables and their relationships are understood early on.

Data import/export

The chances are that you will already have a system of some sort in place, perhaps paper-based or an existing database. If you need to transfer data from a previous database into the new database then the format of the data and the process for transferring it will need to be defined. The transfer may be done in two stages, once at the start of the project (to get realistic quantities of real data) and once at the end (to transfer across the latest live data). Some help from the existing database designer may be required.

Existing data may constrain data in the new database. For example, if order numbers have the form PO/ABC/1234/1999, then the new database may be required to continue this format.

Reports

Database reports may be one of the last things to be considered when writing the requirements specification, probably because they are standalone objects which simply extract data from the database and therefore cannot upset its overall architecture.

If possible, the requirements specification should describe the data to be shown in each report, plus the methods available to the user to apply filters (e.g. to define a date range, or a geographical area). Otherwise, as a minimum, the specification should say how many reports will be designed in total.

Processing

Your database may be simply a repository of data to be entered and retrieved. However, many databases also process or analyse the data. Access is particularly strong in this area, with its excellent object-oriented Visual Basic programming environment. Examples might be:

  • Batch updates of all records in a table. For example, to mark all contacts who have been sent a mail-merge letter
  • Calculation of the labour and material costs at each level in a bill of materials system
  • Execution of algorithms for physically locating delegates at a conference site
  • Complex validation of input data

Technical/performance factors

  • How many users in total?
  • How many concurrent users?
  • The network speed and available bandwidth?
  • The minimum specification of the client hardware. e.g. 266Mhz Pentium II with 64Mb of RAM
  • The specification of the server (back-end) hardware
  • The likely initial size of the main tables and the growth per annum, measured in 1000's of records

Database administration

An operational Access database usually requires less administration than a client-server system. However, it will require attention from time to time. You may decide to appoint someone in house to perform these tasks. It is useful to define up-front how the following will be handled:

  • Database backups
  • User training and support
  • Compact and repair procedures should the database be corrupted
  • Installation of the application on new client machines
  • Addition and deletion of logins; password reset
  • Installation of database upgrades on client machines
  • Feedback of error logs and problems via email or phone

Deliverables

The Requirements Specification should detail what will be delivered. As well as the operational database (front-end and back-end) it may also include a help system, user documentation, release notes, validation results, source code, training, support, utilities, etc.

Schedule

If there are hard deadlines to be met then these should appear in the requirements. There may also be times when access to your site, people or networks is not possible and these should appear as constraints.

 

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Last modified: May 09, 2004