Information about Relational Calculus
The relational calculus refers to the two calculi, the tuple relational calculus and the domain relational calculus, that are part of the relational model for databases and that provide a declarative way to specify database queries. This in contrast to the relational algebra which is also part of the relational model but provides a more procedural way for specifying queries.
The relational algebra might suggest these steps to retrieve the phone numbers and names of book stores that supply Some Sample Book:
The relational calculus would formulate a descriptive, declarative way:
The relational algebra and the relational calculus are logically equivalent: for any algebraic expression, there is an equivalent expression in the calculus, and vice versa.
The relational algebra might suggest these steps to retrieve the phone numbers and names of book stores that supply Some Sample Book:
- Join books and titles over the BookstoreID.
- Restrict the result of that join to tuples for the book Some Sample Book.
- Project the result of that restriction over StoreName and StorePhone.
The relational calculus would formulate a descriptive, declarative way:
- Get StoreName and StorePhone for supplies such that there exists a title BK with the same BookstoreID value and with a BookTitle value of Some Sample Book.
The relational algebra and the relational calculus are logically equivalent: for any algebraic expression, there is an equivalent expression in the calculus, and vice versa.
References
- Date, Christopher J. (2004). An Introduction to Database Systems, 8th, Addison Wesley. ISBN 0-321-19784-4.
See also
- The Third Manifesto
- Tutorial D
- D (data language specification)
- D4 (programming language) (an implementation of D)
Topics in database management systems (DBMS)
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Concepts Database Database models Database storage Relational model Distributed DBMS ACID Null Relational database Relational algebra Relational calculus Database normalization Referential integrity Relational DBMS Primary key, Foreign key, Surrogate key, Superkey, Candidate key | |
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Objects Trigger View Table Cursor Log Transaction Index Stored procedure Partition |
Topics in SQL Select Insert Update Merge Delete Join Union Create Drop Begin work Commit Rollback Truncate Alter |
| Implementations of database management systems | |
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Types of implementations Relational Flat file Deductive Dimensional Hierarchical Object oriented Object relational Temporal XML data stores | |
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Database products Object-oriented (comparison) Relational (comparison) |
Components Query language Query optimizer Query plan ODBC JDBC |
The tuple calculus is a calculus that was introduced by Edgar F. Codd as part of the relational model in order to give a declarative database query language for this data model.
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In computer science, domain relational calculus (DRC) is a calculus that was introduced by Michel Lacroix and Alain Pirotte as a declarative database query language for the relational data model [1].
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The relational model for database management is a database model based on predicate logic and set theory. It was first formulated and proposed in 1969 by Edgar Codd with aims that included avoiding, without loss of completeness, the need to write computer programs to
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Relational algebra, an offshoot of first-order logic, is a set of relations closed under operators. Operators operate on one or more relations to yield a relation. Relational algebra is a part of computer science.
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The Third Manifesto (1995) is Christopher J. Date's and Hugh Darwen's proposal for future relational database management systems that would avoid 'Object-Relational Impedance Mismatch' between object-oriented programming languages and RDBMSs by fully supporting all the capabilities
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D is a set of requirements proposed by Christopher J. Date and Hugh Darwen in their book The Third Manifesto for what they believe a relational database query language ought to be like; D is not a language itself.
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D4 is a computer language used in Dataphor, a truly Relational Database Management System.
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Syntax
Alphora, the creators of D4, have given it a Pascal like syntax. Sample code in D4 made by Alphora is usually written in UpperCamelCase, which is also widely used in Pascal..... Click the link for more information.
A database management system (DBMS) is computer software designed for the purpose of managing databases. Typical examples of DBMSs include Oracle, DB2, Microsoft Access, Microsoft SQL Server, PostgreSQL, MySQL, FileMaker and Sybase Adaptive Server Enterprise.
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database is a structured collection of records or data that is stored in a computer system so that a computer program or person using a query language can consult it to answer queries. The records retrieved in answer to queries are information that can be used to make decisions.
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A data model is not just a way of structuring data: it also defines a set of operations that can be performed on the data. The relational model, for example, defines operations such as select, project, and join.
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flat file database describes any of various means to encode a data model (most commonly a table) as a plain text file.
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Unordered
Unordered storage typically stores the records in the order they are inserted, while having..... Click the link for more information.
The relational model for database management is a database model based on predicate logic and set theory. It was first formulated and proposed in 1969 by Edgar Codd with aims that included avoiding, without loss of completeness, the need to write computer programs to
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A distributed database management system is a software system that permits the management of a distributed database and makes the distribution transparent to the users. A distributed database is a collection of multiple, logically interrelated databases distributed over a computer network.
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ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. In the context of databases, a single logical operation on the data is called a transaction.
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Null is a special marker used to indicate that a data value is unknown in the Structured Query Language (SQL). Introduced by the creator of the relational database model, Dr. E.F.
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A relational database is a database that conforms to the relational model, and refers to a database's data and schema (the database's structure of how that data is arranged).
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Relational algebra, an offshoot of first-order logic, is a set of relations closed under operators. Operators operate on one or more relations to yield a relation. Relational algebra is a part of computer science.
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Database normalization is a technique for designing relational database tables to minimize duplication of information and, in so doing, to safeguard the database against certain types of logical or structural problems, namely data anomalies.
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referential integrity. In this example, there is a foreign key (artist_id) value in the album table that references a non-existent artist — in other words there is a foreign key value with no corresponding primary key value in the referenced table.
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A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. Relational databases are the most common kind of database in use today (assuming one does not count a file system as a database).
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In relational database design, a unique key or primary key is a candidate key to uniquely identify each row in a table. A unique key or primary key comprises a single column or set of columns.
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In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table.
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A surrogate key in a database is a unique identifier for either an entity in the modeled world or an object in the database. The surrogate key is not derived from application data.
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superkey is defined in the relational model of database organisation as a set of attributes of a relation variable (relvar) for which it holds that in all relations assigned to that variable there are no two distinct tuples (rows) that have the same values for the attributes in
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In the relational model, a candidate key of a relvar (relation variable) is a set of attributes of that relvar such that
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- (1) at all times it holds in the relation assigned to that variable that there are no two distinct tuples with the same values for these attributes and
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A database trigger is procedural code that is automatically executed in response to certain events on a particular table in a database. Triggers can restrict access to specific data, perform logging, or audit data modifications.
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In database theory, a view is a virtual or logical table composed of the result set of a query. Unlike ordinary tables (base tables) in a relational database, a view is not part of the physical schema: it is a dynamic, virtual table computed or collated from data in the database.
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table is a set of data elements (values) that is organized using a model of horizontal rows and vertical columns. The columns are identified by name, and the rows are identified by the values appearing in a particular column subset which has been identified as a candidate key.
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In database packages, the term cursor refers to a control structure for the successive (and potential processing) of records in a result set.
A cursor is used for processing individual rows returned by the database system for a query.
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A cursor is used for processing individual rows returned by the database system for a query.
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In the field of databases in computer science, a transaction log (also database log or binary log) is a history of actions executed by a database management system to guarantee ACID properties over crashes or hardware failures.
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