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Definition: The domain of a database attribute is the set of all allowable values that attribute may assume.
Examples: A field for gender may have the domain {male, female, unknown} where those three values are the only permitted entries in that column.
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Advantage of relational model over hierarchical model?
Use of primary keys less data redundancy compatible with inconsistencies associated with database anomalies
What is post relational data model?
A number of extensions to the relational data model have been proposed in the three decades or so since its invention. Many of these extensions have been implemented in commercial DBMS. What is termed the post-relational data model here is not strictly a data model in that no coherent theory has been developed. Nevertheless it is useful to discuss it here in terms of a set of mech- anisms found in many contemporary DBMS. Such a data model is also referred to by the terms extended-relational and object-relational data model. In Chapter 18 we discuss how the proposed SQL3 standard addresses many of these features. In Chapter 34 we also consider how the ORACLE DBMS supports some of these features. In the first half of the chapter we consider two extensions to the data defin- ition part of the relational data model: abstract data types and nested relations. In the second half of the chapter we consider two constructs - triggers and stored procedures - that have been used both for data manipulation and data integrity purposes. The incorporation of these features into a relational DBMS provides it with the ability to handle complex objects and behaviour. Hence many of the DBMS with these features have termed themselves object-rela- tional systems.
Does a relational model provide physical and logical data independence?
Since a user can define a views, logical data independence can achieved by using view definition to hide changes in the conceptual schema. since the sql user has no knowledge of how the data is physically represented, relying solely on the relation abstraction for querying, physical data independence is also achieved.
What is a relational database query and Explain with an example?
A relational database matches data by using common characteristics found within the data set. The resulting groups of data are organized and are much easier for many people to understand.For example, a data set containing all the real-estate transactions in a town can be grouped by the year each transaction occurred, the sale price, a buyer's last name and so on. Such a grouping uses the relational model (a technical term for this is schema). Hence, such a database is called a "relational database."The software used to do this grouping is called a relational database management system (RDBMS). The term "relational database" often refers to this type of software.Relational databases are currently the predominant choice in storing data like financial records, medical records, personal information and manufacturing and logistical data.
What advantages does SQL have over relational algebra?
Generally relational models are queried using relational algebras. SQL and XQuery are examples of relational algebras, with XQuery actually being a purer form of a relational algebra. : XQuery :: + Already exists and supports this extended relational model :: + Supports XPath :: + Supported by Oracle, IBM and Microsoft databases :: + Existing open source implementations for those who don't have it :: - Not yet a standard (but probably will be) :: - Not very easy to formulate :: - Immature development bindings usually resulting in DOM manipulation (not very efficient) :: - Difficult language to optimize which may result in poor performance :: - No developer community :: - No developer tools :: - It's currently a read-only language and the update additions are not focused on transactional systems : SQL :: + Millions of developers know (and love) it :: + Most repositories already support it :: + Supports PROJECTION, JOIN and UNION :: + Long established standard :: + Efficient language bindings with JDBC and ODBC :: + Lots of development tools :: - Need to specify and implement HIERARCHY ENUMERATION :: - Need to work around the multi-value problem with PROJECTION and SELECTION functions
What are the Properties of relational database model?
The relational database model organizes data into relations or tables with rows and columns, providing a clear structure for data storage. It supports the concept of primary keys to uniquely identify each record in a table and foreign keys to establish relationships between tables. Additionally, it ensures data integrity through constraints like referential integrity and data normalization.
What is a table and what role does it play in the relational model?
A table in the relational model is a data structure that stores information in rows and columns. It serves as the fundamental unit for organizing and storing data in a database. Tables enable the representation of relationships between entities and facilitate efficient querying and manipulation of data.
In the context of the Capital Asset Pricing Model how would you define beta How are beta determined and where can they be obtained What are the limitations of beta?
In the context of the Capital Asset Pricing Model how would you define beta? How are beta determined and where can they be obtained? What are the limitations of beta?
Does the Microsoft Access use a relational or flat-file model?
Access can use a relational model of a database design.
2 Explain why navigation is simple in Relational Data Model than in Hierarchical?
Explain why nevigation is simple relational data model than in hirarchical model
What is the most popular database model?
Relational Database Model
How is relational model better than traditional file processing?
The relational model offers better data organization through its structured tables with defined relationships between them, facilitating data consistency and integrity. It also allows for more efficient querying and retrieval of data using SQL, compared to the sequential file access in traditional file processing systems. Additionally, the relational model supports normalization to reduce data redundancy and improve data maintenance.
Compare between network hierarchal and relational model?
1. Relational Model : Newer database model; Network Model - Older database model 2. The network model structures data as a tree of records with each record can have multiple parent and child records, forming a lattice structure. The basic data structure of the relational model is the table, where information about a particular entity (say, an employee) is represented in columns and rows 3.The relational model has strong mathematical foundation with set theory and predicate logic. Network Model has no strong mathematical background. 4. Relational model is the most flexible of the database models. Network model is not very flexible. 5. Relational model has widespead use. Network model has limited use.
What is ER models?
The Entity-Relationship Model is often referred to as a semantic data model, because it more closely resembles real world scenarios than, e.g., the relational model. . In the ER model, we model the concept of "Instructors." In the relational model we deal with names and phone numbers. . In the ER model, there is a distinction between entities (objects) and relationships between such entities. In the relational model, both concepts are represented by relations.
What is relational in relational model?
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. Most popular commercial and open source databases currently in use are based on the relational model. A short definition of an RDBMS may be a DBMS in which data is stored in the form of tables and the relationship among the data is also stored in the form of tables.
Differentiate between the E-R model and Relational model?
The E-R model (Entity-Relationship model) is a visual representation of entities, attributes, and relationships in a database, while the relational model organizes data into tables with rows and columns. The E-R model focuses on the logical design of a database, while the relational model focuses on the physical implementation of data storage and retrieval. E-R model uses entities, attributes, and relationships to depict data structures, while the relational model uses tables, keys, and relationships to organize data.
What is E-R data model?
The Entity-Relationship Model is often referred to as a semantic data model, because it more closely resembles real world scenarios than, e.g., the relational model. . In the ER model, we model the concept of "Instructors." In the relational model we deal with names and phone numbers. . In the ER model, there is a distinction between entities (objects) and relationships between such entities. In the relational model, both concepts are represented by relations.
