Relational databases and schemas - class-XII

In database terminology, a relation (table) is identified by its name, while its structure and constraints are defined by its schema. Therefore, the name provides the identity and the schema provides the description.

In the relational data model, a column header represents an attribute of the entity. Since 'attribute' is not listed as an option, 'None of the above' is the correct choice.

In relational data model, the table name and column names are used to help in interpreting the meaning of values in each row. All values in a column, which belong to a particular domain, are of same data type. A column header is called an attribute.

Database has two important properties (or characteristics): one is integrated and second is shared. Integrated property implies that distinct data tables have been logically organised. The purpose is to reduce or eliminate redundancy (or duplicity) and also to facilitate better data access.

A relational database is a type of database that stores and provides access to data points that are related to one another. Relational databases are based on the relational model, an intuitive, straightforward way of representing data in tables.

The relational data model represents a table of values (or data table). Each row of the table, therefore, represents a collection of related data values and hence typically corresponds to real world entity or relationship. Formally, a row is called a tuple.

Database has two important properties (or characteristics): one is integrated and second is shared. The shared property means that all those who are authorised to use data/information have access to relevant data.

Information refers to data that have been processed and organised in a form, which is suitable for decision-making, The raw data processed in accordance with decision usefulness of a decision-maker becomes information.

Among several representational models, Relational Data Model (RDM) is the most popular and widely used in actual practice. It represents the database as collection of relations, which resembles a table of values (or data table).

The data type describing the types of values (such as text value, numeric values, data values, currency value, etc.) that can appear in each column is called a domain. A domain is a set of indivisible values.

An attribute is fully functional dependent on another attribute, if it is Functionally Dependent on that attribute and not on any of its proper subset. For example, an attribute Q is fully functional dependent on another attribute P, if it is Functionally Dependent on P and not on any of the proper subset of P.

There are four different constraints, which can be specified on relational databases. They are domain constraints; key constraints; entity integrity constraints and referential integrity constraints.

A relation represents an entity type. A relation (or relation state) is a set of tuples wherein each tuple is an ordered list of values corresponding to attributes of relation.

The relational data model represents the database as collection of relations, which resembles a table of values (or data table). The table name and column names are used to help in interpreting the meaning of values in each row. Each row of a table is called a data record.

A relational database schema is a set of relation schemas and a set of integrity constraints. A relational database state is a set of relation state such that every relational database state satisfies the integrity constraints specified on relational database schema.

Entity integrity constraint is one of the constraints on relational database. It states that no primary key value can be null because it is used to identify individual tuple in a relation. Null value implies that we cannot identify such tuples or identify these as alike. A failure to distinguish them means they are duplicates.

It is a merit for special consideration. The integrity constraints, specified on database schema, must hold in every database state of that schema.

Each value in a tuple is an indivisible value to imply that it is not divisible into components within the framework of the basic relational model. This implies that composite and multi-valued attributes are not allowed. A special value called Null is used to represent unknown or not applicable values of attributes in a tuple.

While key and entity constraints are specified on individual relation, the referential integrity constraint is specified between two or more relations. This constraint is specified to maintain consistency among the tuples in such relations.

Each data record, which corresponds to a tuple of a relation, in a table must be distinct. Every relation has at least one key by default, which is the combination of all its attributes. This key is called super-key by default.

Minimal super-key (also called Key) is defined as that part of super-key from which any attribute cannot be removed without sacrificing the uniqueness constraint.

Minimal super-key is also called as Key. It is defined as that part of super-key from which any attribute cannot be removed without sacrificing the uniqueness constraint.

There are three basic types of updates: insert, delete and modify. Delete operation is carried out to remove a tuple from a relation. A particular data record from a table can be removed by performing such a operation. The delete operation can violate only referential integrity, if tuple being removed is referenced by foreign key from tuples in the database.

There are two categories of operations on relational model: updates and retrieval operation on Relational Data Model does not cause violation any integrity constraints. 

A relational database schema is a set of relation schemas and a set of integrity constraints. There are four different constraints, which can be specified on relational database. These are: domain constraints, key constraints, entity integrity constraints, referential integrity constraints. 

The relational data model represents the database as collection of relations, which resembles a table of values (or data table). Each row of the table, therefore, represents a collection of related data values and hence typically corresponds to real world entity or relationship. Among several representational models, Relational Data Model (RDM) is the most popular and widely used in actual practice. 

The domain is one of the constraints, which can be specified on relational databases. The value of each attribute of a relational must be an indivisible value and drawn out of possible values associated with its domain. The value of an attributed, therefore, must conform to the data type associated with the domain.

A relational database schema is a set of relation schemas and a set of integrity constraints. A relational database is a set of relation states such that every relational database state satisfies the integrity constraints specified on relational database schema.

The relational model organizes data into tables (relations) consisting of rows and columns. This structure is the foundation of relational database management systems.

While key and entity constraints are specified on individual relation, the referential integrity constraints is specified between two or more relations. This constraint is specified to maintain consistency among the tuples of such relations.

A relational database schema is a set relation schemas and integrity constraints. It is a set of relation states such that relational database state satisfies the integrity constraints specified on relational database schema. There are two categories of operations on relational model: updates and retrieval. Update operation are of three basic types i.e. insert, delete and modify. Retrieval operation on relational data model does not cause violation of any integrity constraints.