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The theory of relational databases
The document discusses key concepts in relational database models including: - Data is stored in tables called relations with rows and columns where rows represent records and columns represent attributes. - Relations can be normalized to eliminate redundant data and optimize storage. - Database normalization involves organizing data into tables through a multi-step process to remove anomalies. - SQL is a programming language used to interact with relational databases through operations like joins, transactions, and indexing/hashing techniques.
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The theory of relational databases
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- 2. Relational Model The mainhighlights of this model • Data is stored in tables called relations. • Relations can be normalized. • In normalized relations, values saved are atomic values. • Each row in a relation contains a unique value. • Each column in a relation contains values from a same domain.
- 3. Concepts Concepts Tables − Inrelational data model, relations are saved in the format of Tables. This format stores the relation among entities. A table has rows and columns, where rows represents records and columns represent the attributes. Tuple − A single row of a table, which contains a single record for that relation is called a tuple. Relation instance − A finite set of tuples in the relational database system represents relation instance. Relation instances do not have duplicate tuples. Relation schema − A relation schema describes the relation name (table name), attributes, and their names. Relation key − Each row has one or more attributes, known as relation key, which can identify the row in the relation (table) uniquely. Attribute domain − Every attribute has some pre-defined value scope, known as attribute domain.
- 4. Normalization Database Normalization isa technique of organizing the data in the database. Normalization is a systematic approach of decomposing tables to eliminate data redundancy. It is a multi-step process that puts data into tabular form by removing duplicated data from the relation tables. Normalization is a method to remove all anomalies and bring the database to a consistent state.
- 5. First Normal Form FirstNormal Form is defined in the definition of relations (tables) itself. This rule defines that all the attributes in a relation must have atomic domains. The values in an atomic domain are indivisible units.
- 6. Second Normal Form Asper the Second Normal Form there must not be any partial dependency of any column on primary key. It means that for a table that has concatenated primary key, each column in the table that is not part of the primary key must depend upon the entire concatenated key for its existence.
- 7. Third Normal Form Fora relation to be in Third Normal Form, it must be in Second Normal form and should not be non-prime attribute is transitively dependent on prime key attribute.
- 8. SQL Overview SQL isa programming language for Relational Databases. It is designed over relational algebra and tuple relational calculus. SQL comes as a package with all major distributions of RDBMS.
- 9. SQL Joins Join isa combination of a Cartesian product followed by a selection process. A Join operation pairs two tuples from different relations, if and only if a given join condition is satisfied.
- 10. Transactions A transaction canbe defined as a group of tasks. A single task is the minimum processing unit which cannot be divided further.
- 11. Indexing Indexing is adata structure technique to efficiently retrieve records from the database files based on some attributes on which the indexing has been done.
- 12. Hashing Hashing uses hashfunctions with search keys as parameters to generate the address of a data record.
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