Users

If an information system is:
'A computer system with the primary purpose of supporting the information requirements of its users.'
Then a user must be:
'A person whose information requirements are being supported.'

Some users will have varying requirements, although some groups may have identical needs. A user of a single-user sytem may find that his needs change over time or through use. Single user systems have the same characteristics as multiple user systems. There is no interaction between users in a multi-user system, therefore each user can be seen as a single user, they only interact with the system.

A user in a multi-user system will only be aware of changes if he had direct knowledge of the state of the system before it is changed by another user. There should only be a single copy of the database. If any individual needs access to data, it should be the same data that is available to all users. Such a database is a shared collection of data.

Not all data within the collection will be shared. Don't forget that users will be granted access only to their own user-view of the data, via the application processes.

User Processes

The means by which the user accesses the database. This can be through an application process designed and constructed for one purpose. It cannot be changed. A second method is with a database tool. Such tools allow for the construction of database queries in order to retrieve data, update data or displaying and printing reports from the data. There may also be application development tools for constructing database application processes.

Scalability

Increasing the scale of some aspect of a system. A feature of a small system is applicable to large systems. Some systems can be complex and may be vast in size, holding unimaginable amounts of data. Hundreds of users may need simoultaneous access to the same data. Users should not have to wade through stacks of data to get at what they need. The application process must be tailored to provide only the data that satisfies their requirements.

Management

Users have no understanding of a complete system but have specific requirements of the characteristics of the system. A database must be reliable. In event of a catastrophic failure and subsequent loss of data, measures must be in place to provide a recovery of all data within the database. Incomplete transactions will be ignored for the purposes of recovery. they may lead to inconsistencies.

The database should be secure, allowing access to data to only those users authorized for the specific task. Whether it be using data or updating it, access control facilities must be used to protect data.

The database should have integrity. The data should be trustworthy and held within the correct semantic constraints. All users should share the same data to which they have access, not differing versions of the same data. (One table not two!)

Duplication of information can cause inconsistency. Users have a responsibility to ensure that data is correct. Access controls restrict updating to those with the relevant knowledge of maintaining data correctness.

Concurrency enables many users to access a database independent of others. It should also give the user the perception that the data is available at any time unaffected by other users accessing the same data.

People

Database Administrator (DBA) - Controls and administers the database system. May be a department or individual.

Application Developer - Provides application processes to suit the user(s).

Change

Data may change as it is updated, but the important change to consider is the way that the user may require a different view of the data. The database itself may not change but the application process may require updating or renewing.

There may be a need for more data. This will result in changes to the database and new application processes.

Change could forced by the environment of the database, new law or a need to improve the system.

Data types, data structure and information

A data type is a set of values, with operations on those values. As in integers with -, +, *, etc. Or strings of text characters that can be indexed, compared etc. Objects are data types where the data is encapsulated for manipulation by defined operators. In a database all data belongs to a data type.

The organisation of data within a database is referred to as it's structure. This structure, also forms the basis of how the data can be searched. the structure used in this course is a special kind of table. This particular kind of table is called a relation. A database is formed of numerous tables, with each split into columns and rows.

The rules that govern the interpretation of each row within a table are the same. Tables have uniformity. Each column would have values of the exact same data type. Tables are also restrictive. Any new kind of data would require additonal columns within the table.

Comments, suggestions, ideas to
Stuart Banner