Creating a Database that Meets User Needs 3: The Requirements Phase

Computer Storage

After the scope of a database development project has been established during the Definition Phase, you need to find out what the stakeholders in the project need it to do for them. That is the job of the Requirements Phase. In the Definition Phase, you talk with the client. This is the person who has the authority to hire you or, if you are already an employee, assign you to this development task. This person is not, however, the only one with an interest in the project. In all probability, someone other than the client will use the system on a daily basis. Even more people may depend on the results generated by the system. It is important to find out what those people need and what they prefer because your primary client may not have a complete understanding of what would serve them best.

The amount of work you must do in the Requirements Phase depends on the client. If can be quick and easy if your are dealing with a client who has prior experience with similar database development projects. Such a client has a clear idea of what he wants and, equally important, what is feasible within the time and budget constraints that apply.

On the other hand, this phase can be difficult and drawn-out if the client has no experience with this kind of development, only a vague idea of what he wants, and an even vaguer idea of what can reasonably be done within the allotted time and budget.

Aside from your primary client, other stakeholders in the project, such as various users, managers, executives, and board members, also have ideas of what they need. These ideas often conflict with each other. Your job at that point is to come up with a set of requirements that everyone can agree upon. This will probably not meet everyone’s desires completely. It will be a compromise between conflicting desires, but will be the solution that gives the most important functions to the people who need them.

The Statement of Requirements

The Statement of Requirements is an explicit statement of the database application’s deliverables, including its display, update, and control mechanisms. It will answer such questions as:

  • What will the display look like? How will components be arranged? What will be the color scheme?
  • What items will need to be updated, and how will that be done?
  • How will users navigate between screens?
  • Will selections be made by key depressions, and if so, which  keys will do what?
  • Will operations be initiated by mouse clicks? If so, which operations?
  • What will the maximum acceptable response time to a query be?

The Statement of Requirements must be as detailed as possible because it is essentially a contract between you and your client. You are agreeing on exactly what will be delivered and when it will be delivered. To seal the arrangement, bot you and your client should sign the Statement of Requirements, signifying agreement on what you will be responsible for delivering.

Sumarizing, in the Requirements Phase you must:

  • Interview typical members of all classes of stakeholders in the project.
  • Provide leadership in getting stakeholders to agree on what is needed.
  • Create the Statement of Requirements, which describes in detail what the system will look like and what it will do.
  • Obtain client approval of the Statement of Requirements, indicated by a signature and date.

Creating a Database that Meets User Needs 2: The Definition Phase

Computer Storage

In the first installment of this series of posts I said that for a development effort to succeed in meeting its objectives, a series of steps should be taken, each one building upon the previous ones, without leaving any out. This series of steps or phases is called the System Development Life Cycle (SDLC). The phases are:

  • The Definition Phase
  • The Requirements Phase
  • The Evaluation Phase
  • The Design Phase
  • The Implementation Phase
  • The Final Documentation and Testing Phase
  • The Maintenance Phase

Rookie developers often, after receiving a development assignment, start building the database and its associated application. Unfortunately, that is what should be done in the Implementation Phase. They have just skipped the first four phases of the SDLC and consequently, their chance of success is minimal. It is really important to go through all the phases and to perform all the tasks within each phase.

Every phase is important, but the Definition Phase is crucial, because if you don’t define the task properly at the beginning, there is no chance that the final product will meet your client’s needs.

There are five major tasks that must be performed as part of the Definition Phase. They are:

  • Define the task to be performed. A database project begins when a person or group realizes that they have a problem and that a database is probably part of the solution of that problem. Depending on how experienced they are with such things, they may have a very clear idea of what the database should be and how it should perform, or they may have only a vague notion of what is needed. If you are called in to be the developer of this project, it is up to you to develop a detailed definition of exactly what the product of the development effort will do.
  • Determine the scope of the project. In addition to defining the task to be performed, at this point you also want to estimate how big the project is. What equipment will be needed? How much system analyst time will it take? How much programmer time? What is the required completion date?
  • Perform a feasibility analysis. The client has an idea of what she wants, when she wants it, and how much she is willing to pay for it. It is up to you to determine whether the project can be completed at all, given those constraints. If you determine that you cannot meet the requirements, you can negotiate for more time, more budget, or fewer features, or you can graciously decline to take the job.
  • Form a project team. You might be able to complete a simple project by yourself, but for a big project on a tight deadline, you should build a team, where each member works on the part of the overall task that they are best qualified to address. Network with fellow professionals so that when jobs arise, you have a pool of qualified people you can draw from for a development team.
  • Document everything. One important part of a development project that is often not given the attention it deserves is the documentation of what is learned and what is done.  Seemingly, documentation is a side issue, perhaps to be taken up after the “real” work of producing the database is done. Nothing could be further from the truth. Documenting every step along the way is vital. It is the only way to keep things on track, starting with the initial specification of what the project is supposed to do and ending with the post mortem after it is finally retired for good. On countless occasions, you will find that detailed documentation will keep you from going down the wrong path, and often it will save you from the database becoming unmaintainable when a key team member leaves.
  • Get the client to approve the Definition Phase document, in writing. It is important that you and your client be of one mind about exactly what the task is that you have been engaged to perform. Documenting exactly what you will provide (the deliverables) protects you both. It’s not uncommon for a client to tell you what you want, and then after you deliver it, say “Oh, but I thought we had agreed that you would also provide the “X” capability.” Fill in whatever you want for X. This all too common experience is called scope creep. The client wants you to do more, but does not want to pay you more for it. Your best defense is to get the client to sign the Definition Phase document at the conclusion of the Document Phase, before you start work in earnest on the project. If any additional work is desired beyond what is specified in the document, you are in a strong position to ask for additional payment.

Creating a Database that Meets User Needs

Computer Storage


A database is a repository for some person’s or organization’s data. For it to meet user needs, it must satisfy several criteria:

  • It must be easy to enter new data into it.
  • It must be easy and fast to retrieve just the information you want from it.
  • It must store the data in such a way that database operations do not corrupt it.

A database system consists of the hardware the database resides on, the operating system that controls that hardware, the database management system (DBMS) that performs operations on the database, the database application that translates the user’s commands into instructions the DBMS understands, and the database itself.

The database application is the part of the system that interfaces directly with the user, so it is the part that must make it easy to enter new data, and easy and fast to retrieve the desired information. This is the part of the system that database developers create. The DBMS comes from a vendor such as Microsoft or Oracle or from a consortium of professionals as is the case for open source DBMSs such as PostgreSQL or MySQL. The operating system (OS) comes from an OS vendor, such as Microsoft, or from an open source community, as is the case with Linux. Finally, the hardware comes from a hardware vendor such as IBM, Dell, or HP.

The hardware, operating systems, and DBMSs are all general purpose and have proven to be reliable in the marketplace. For these things, you can just buy the components that have enough capacity to meet your needs. The custom part is the database application. This is the software piece that solves the particular problem that you have. Since your needs are not exactly like anyone else’s you are either going to have to produce this part yourself, or hire someone to do it. Even if you decide to hire someone, it is good to understand what’s important so that you can make sure that what is finally produced actually does meet your needs.

There is a time-tested method for making sure that an application that results from a development effort actually meets the needs of those who will be using it. That method, which guides developers through the entire life of the development project is called the System Development Life Cycle (SDLC). The SDLC breaks down the development effort into a sequence of phases that, when carefully followed give a high probability of a successful project. The SDLC is not restricted to database development. It applies to development projects of any kind.

The phases are:

  • Definition
  • Requirements
  • Evaluation
  • Design
  • Implementation
  • Final Documentation and Testing
  • Maintenance

Each phase is important and skipping any one of them can cause the entire project to fail. I will describe each of these phases in detail in subsequent posts, including why it is important.

How a DBMS Organizes Database Data for Speedy Retrieval

Computer Storage

It’s important that database data be retrievable in a reasonable amount of time. This is particularly an issue for very large databases. The speed with which information is retrieved from a database depends on a number of factors. The size of the database and the speed of the hardware it is running on are obvious factors. Perhaps most critical, however, is the method used to access table data, which depends on the way the data is structured on the storage medium.

How quickly a system can retrieve desired information depends on the speed of the device that stores it. Different storage devices have a wide range of speeds, spanning many orders of magnitude. For fast retrievals, the information you want should reside on the fastest devices. Because it is difficult to predict which data items will be needed next, you can’t always make sure the data you are going to want next will be contained in the fastest storage device. Some storage allocation algorithms are nonetheless quite effective at making such predictions.

There is a hierarchy of storage types, ranging from the fastest to the slowest. In general, the faster a storage device is, the smaller its capacity. As a consequence, it is generally not possible to hold a large database entirely in the fastest available storage. The next best thing is to store that subset of the database that is most likely to be needed soon in the faster memory. If this is done properly, the overall performance of the system will be almost as fast as if the entire memory was as fast as the fastest component of it. Here are the components of a typical memory system, starting with the fastest part:

Registers: The registers in a computer system are the fastest form of storage. They are integrated into the processor chip, which means they are implemented with the fastest technology and the delay for transfers between the processing unit and the registers is minimal. It is not feasible to store any portion of a database in the registers, which are limited in number and in size. Instead, registers hold the operands that the processor is currently working on.

L1 cache: Level 1 cache is typically also located in the processor chip, but is not as intimately integrated with the processor as are the registers. It is the fastest form of storage that can store a significant fraction of a database.

L2 cache: Level 2 cache is generally located on a separate chip from the processor. It has greater capacity and is usually somewhat slower than the L1 cache.

Hard disk: Hard disk storage has orders of magnitude more capacity than does cache and is orders of magnitude slower. This is where databases are stored. Registers, L1 cache, and L2 cache are all volatile forms of memory. The data is lost when power is removed. Hard disk storage, on the other hand, is non-volatile. The data is retained even when the system is turned off. Because hard disk systems can hold a large database and retain it when power is off or interrupted, such systems are the normal home of all databases.

Offline storage: It is not necessary to have immediate access to databases that are not in active use. They can be retained on storage media that are slower than hard drives. A sequential storage medium such as magnetic tape is fine for such use. Data access is exceedingly slow, but acceptable for data that is rarely if ever needed. Huge quantities of data can be stored on tape. Tape is the ideal home for archives of obsolete data that nevertheless need to be retained against the day when they might be called upon again.


Business users who just want to retrieve the information they need from a database need not concern themselves with how the DBMS does it. However, it is good to know what is going on “under the covers” to return to you the results you want in a timely fashion.

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