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Computing Paper 2: Database concepts (1.3.2)
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- 1What is a relational database?An organised collection of data in tables.
- 2What is an entity?Row in table stores data of specific entity.
An object in real world e.g. person, even thing. Physical or conceptual existence. - 3What is an attribute/field?Each column in table represents attribute.
A property of an entity. - 4What is a flat file database?A single file of one table with data. E.g. spreadsheets, text files.
- 5What is a primary key? What is a secondary key?Unique identifier of each entity. An attribute or set of attributes. E.g. CustomerID.
Other attributes that can be used to identify an entity. E.g. surname, email. - 6What is a foreign key? What is a composite key?An attribute that can join two tables. E.g. subject table to a student table using StudentID.
Combination of attributes to uniquely identify an entity.
E.g. SubjectID and Subject. - 7If there is a many-to-many relationship between two tables, what must you do?Link an extra table between the original two to connect them.
E.g. Student - Courses
Student - Enrolment - Courses - 8What is referential integrity?Ability of database to keep related data from being corrupted while maintaining relationships between tables.
-Ensuring use of a valid primary key.
-Preventing deletion of related attributes to key being deleted.
-if key updated, attribute related is too. - 9What is indexing?In order to locate primary keys quickly in a database, an index of primary keys with the position of each record.
Can also search using secondary indexes. - 10What is normalisation?Process to reduce data duplication and improvement in referential integrity.
There are 3 stages of normalisation. - 111NF-Removes repeating attributes & groups of attributes.
-Data is atomic (updates/deletion as a whole)
-Each record has primary key.
Use link table- add 3rd table. - 122NFRemove partial dependencies (attributes depend on only part of the primary key). This can only occur if primary composite key.
- 133NFRemoves 'non-key dependencies' (when value of attribute is determined by another attribute which is not a part of the key).
- 14ACID Atomicity: Consistency:Atomicity is the concept that the components of a transaction are atomic, Processed in its entirety or not at all.
Ensure that any illegal transaction is rejected so that the integrity of the database is upheld. Cannot violate any defined rules. - 15ACID Isolation: Durability:Ensure that each transaction will be isolated and dealt with in a way that does not affect others.
Ensures data is saved once transaction has been completed. Even if hardware failure after a transaction, the data will be safe. - 16SerialisationSerially: one transaction after another.
Cannot use w/ databases as result in poor response time, transactions need to queue.
Serialisation: If transactions run concurrently (overlapping time periods), the effect should be the same as if executed serially. - 17Record lockingAllows concurrent transactions, records locked until update complete.
Deadlock: When a requested system resource is locked which in turn the other is trying to do the same. - 18Timestamp orderingTransaction has 2 timestamps: when record last read & when record last written or updated. Stamps for read or write also.
When read/write takes place, checks write/read stamp. If different then last save, knows another transaction taking place on record. - 19Commitment orderingBlocks requests until current transaction is completed. Prevents losing updates to record.
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- A level (Computing Paper 2) Computing Fichas sobre Computing Paper 2: Database concepts (1.3.2), creado por Qashrina Collier el 11/05/2021.
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- Qashrina Collier
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