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Computing Academy GCSE Computer Science

DBMSs can lock a record

DBMSs can lock a record if it is currently being accessed by another user to prevent this problem from occurring. Once a record has been locked by one user, other users cannot edit that record. There is usually a time limit on record locking. When booking tickets the user may be given a limited amount of time to make payment (as illustrated in the previous image) during which the record for those seats in the database is locked to prevent anybody else from purchasing them. Once the time has elapsed, if the user has not made payment, the database record for those seats would be unlocked and they would become available for another user to purchase. Record locking prevents concurrency problems and conflicting updates. Data Integrity If a person has integrity it means you can take them at face value: they are honest and true. Data integrity means that the data is accurate, valid and as expected. If data is entered incorrectly into a DBMS, or if that data is not processed correctly integrity is lost. 135

When entering data into a computer system to be stored in a DBMS validation checks can be performed on the data to assure the integrity of the data. Validation Check Format Length Lookup Presence Range Type Description Date of Birth is usually entered as “DD / MM / YYYY”. Entering “01 / CB / QM34” would cause the format validation check to fail as only numbers were expected. UK telephone numbers are no longer than 11 digits long. Entering 12 or more digits for a telephone number field would cause a length check to fail. When entering a car registration, for example, a lookup check might be performed to check the registration against a list to ensure that the registration actually exists. This check looks to see if each field has been completed. If a telephone number or email address field has been left blank, the presence check will fail. A range check ensures the data entered is within a valid range. A valid range for age might be 1-110. Somebody inputting their age as 130 is likely to be entering invalid data. A telephone number will have up to 12 digits and no letters. Entering letters in a telephone number field will cause the type check to fail. Verification is another method of ensuring data integrity and is often used along with validation. Typing in the same piece of data twice (such as when confirming a password) is an example of verification - it’s there to make sure you don’t accidentally press the wrong key. Data Redundancy Within organisations there are often several departments: in a hospital for example, there are wards specialising in the heart, the brain, fractures and bones etc. If a patient visited several wards in a hospital and each ward created a new database record for the patient data would be duplicated. Even if the patient only even visited one 136

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