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| all articles of clothing which come in the color blue. The most common query language used to access database systems is the Structured Query Language (SQL). The DBMS also provides security features that protect against unauthorized users trying to gain access to confidential database information; and prevent data loss in case of a system crash. Depending on the settings, users are allowed access to either all, or specific database subschemas, through the use of passwords. For example, while a database may contain detailed customer [DBMS] information, certain users may only be allowed access to customer names and addresses, while others may be able to view payment specifications. Access and change logs can be programmed to add even more security to a database, recording the date, time and details of any user making any alteration to the database. Furthermore, the DBMS is also responsible for the database’s integrity, ensuring that no two users are able to update the same record at the same time, as well as preventing duplicate entries, such as two employees being given the same employee number. Database information normally consists of subjects, such as customers, employees or suppliers; as well as activities such as orders, payments or purchases. This information must be organized into related record types through a process known as database design. The DBMS that is chosen must be able to manage different relationships, which is where database models come in. Hierarchical databases organize data under the premise of a basic parent/child relationship. Each parent can have many children, but each child can only have one parent. In hierarchical databases, attributes of specific records are listed under an entity type and entity types are connected to each other through one-to-many relationships, also known as 1:N mapping. Originally, hierarchical relationships were most commonly used in mainframe systems, but with the advent of increasingly complex relationship systems, they have now become too restrictive and are thus rarely used in modern databases. |
The proven process we use for developing database systems requires the following stages; 1. Establishing and using a project management methodology. We use PRINCE 2 practitioners for this work. Other methodologies can be used if required. 2. Initiating the project and establishing its benefits. This includes determining the feasibility of achieving those benefits. 3. Production of logical and physical data models to meet the stated requirements. In this stage a testing plan is established. Data input (including initial loading of data) and data output is defined so that testing can prove that the system is logically correct. |
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