ORACLE DBA

Functional Dependency Functional dependency (FD) is a set of constraints between two attributes in a relation. Functional dependency says that if two tuples have same values for attributes A1, A2,..., An, then those two tuples must have to have same values for attributes B1, B2, ..., Bn. Functional dependency is represented by an arrow sign (→) that is, X→Y, where X functionally determines Y. The left-hand side attributes determine the values of attributes on the right-hand side. Armstrong's Axioms If F is a set of functional dependencies then the closure of F, denoted as F+, is the set of all functional dependencies logically implied by F. Armstrong's Axioms are a set of rules, that when applied repeatedly, generates a closure of functional dependencies. Reflexive rule − If alpha is a set of attributes and beta is_subset_of alpha, then alpha holds beta. Augmentation rule − If a → b holds and y is attribute set, then ay → by also holds. That is adding attribut...

If a database design is not perfect, it may contain anomalies, which are like a nightmare for any database administrator. Managing a database with anomalies is next to impossible.There are different types of anomalies which can occur in referencing and referenced relation which can be discussed as: Insertion anomaly We tried to insert data in a record that does not exist at all. Deletion anomalies  We tried to delete a record, but parts of it was left undeleted because of unawareness, the data is also saved somewhere else. Update anomalies  If data items are scattered and are not linked to each other properly, then it could lead to strange situations. For example, when we try to update one data item having its copies scattered over several places, a few instances get updated properly while a few others are left with old values. Such instances leave the database in an inconsistent state. Normalization is a method to remove all these anomalies and bring the da...

Although DBMS & RDBMS both are used to store information in physical database, but there are some remarkable differences between them. The main differences between DBMS & RDBMS are given below - DBMS 1.  DBMS applications store data on file. 2. In DBMS, data is generally stored in either hierarchical form or a navigational form. 3. Normalization is not present in DBMS. 4. DBMS does not apply any security with regards to data manipulation. 5. DBMS uses file system to store data, so there will be no relation between the tables. 6. DBMS has to provide some uniform methods to access the stored information. 7. DBMS does not support distributed database. 8. DBMS is meant to be for small organization and deal with small data. It supports single user. 9. Example of DBMS are file systems, XML etc. RDBMS 1. RDBMS application store data in tabular form. 2. In RDBMS, the tables have an identifier called primary key and the data values are stored in the form o...

What is Database ? Database is a collection of related data and data is a collection of facts and figures that can be processed to produce information. What is DBMS ? A database management system stores data in such a way that it becomes easier to retrieve, manipulate, and produce information. RDMS A relational database management system (RDBMS) is a program that lets you create, update and administer a relational database. Most  commercial RDBMS's use the Structured Query Language (SQL) to access the database, although SQL was invented after the development of the relational model and is not necessary for its use. Relational Database A relational database is a collection of data item organised as a set of formally described tables from which data can be accessed or reassembled in many different ways without having recognize the database tables. The relational database was invented by E.F.Codd at IBM in 1970. The main highlights of this model are - 1. Data is store...