Hashed file organisation is also called a direct file organisation.In this method, for storing the records a hash function is calculated, which provides the address of the block to store the record. Any type of mathematical function can be used as a hash function. It can be simple or complex.Hash function is applied to columns or attributes to get the block address. The records are stored randomly. So, it is also known as Direct or Random file organization.If the generated hash function is on the column which is considered as key, then the column can be called as hash key ... Read More

In secondary Index (Unique value) is created for each record in a data file which is a candidate key. Secondary index is a type of dense index and also called a non clustering index.Secondary mapping size will be small as the two levels DB indexing is used.While creating the index, generally the index table is kept in the primary memory and the main table is kept in secondary memory because of its size.A table may contain thousands of records for this reason the sparse index becomes so large which cannot be handled in primary memory.Also, if we cannot keep the ... Read More

Different organizations have struggled with their management information systems and their membership databases. The main struggle here is the lack of centralized information. Too often, assurance and non-profits keep separate databases for membership, events, sales, and other processes. When at all feasible, these databases should be combined into a single, centralized database.Advantages of centralized database over other databasesThe advantages of centralized database over other databases are explained below −Data integrity − In a centralized database the data integrity is maximized and data redundancy is minimized, as the single storing place of all the data also implies that a given set ... Read More

A Clustered index is one of the special types of index which reorders the way records in the table are physically stored on the disk. It sorts and stores the data rows in the table or view based on their key values. It is essentially a sorted copy of the data in the indexed columns.Sometimes we are asked to create an index on a non-unique key like dept-id in the below table. There could be several employees in each department. Here, all employees belonging to the same dept-id are considered to be within a single cluster, and the index pointers ... Read More

In the primary index there is a one-to-one relationship between the entries in the index table and records in the main table. Primary index is used on a primary key.Types of Primary IndexPrimary index are of two types, which are as follows −Dense Primary IndexIn a dense primary index an index record appears for every search key value in the main table that means each and every record in the main table has an entry in the index.ExampleGiven below is an example of dense primary index −A pointer stores the address of a record.Non-Dense / Sparse Primary indexAn index record ... Read More

A Database Management System (DBMS) is a mix of computer software, hardware, and data intended to electronically control information by means of computer preparation.Two sorts of database management systems are DBMS and FMS.In straightforward terms, a File Management System (FMS) is a Database Management System that enables access to single records or tables at once.FMS oblige level records that have no connection to different documents.The FMS was the ancestor for the Database Management System (DBMS), which enables access to various records or tables at once.We have to utilize circle stockpiling for the database, and to exchange pieces of information between ... Read More

File organization is the way of storing data in the file. It is very useful as it determines ways of accessing it, storing it while maintaining the flexibility of the system.Role of file organizationHence, the roles of file organization are as follows −It provides flexibility.Easy access of data in files.Easy storage.Decrease the complexity of the overall system and files are stored and well maintained.Provide security to data.Saves users time in searching for particular information / data in file as every data is arranged so nicely.MethodsThe methods of file organization are as follows −ContiguousData and files are arranged in contiguous address ... Read More

Let us begin by understanding the hashed file organisation.Hashed File OrganisationHashed file organisation is also called a direct file organisation.In this method, for storing the records a hash function is calculated, which provides the address of the block to store the record. Any type of mathematical function can be used as a hash function. It can be simple or complex.Hash function is applied to columns or attributes to get the block address. The records are stored randomly. So, it is also known as Direct or Random file organization.If the generated hash function is on the column which is considered as ... Read More

Indexing is one of the techniques used to optimize performance of a database by reducing the number of disk accesses that are required when a query is processed.A database index is a data structure that is helpful to quickly locate and access the data in a database table.Indexes are created using database columns.The first column is the Search key which contains a copy of the primary key or candidate key of the table.The second column is the data reference that contains a set of pointers which hold the address of the disk block where the key value can be found.Structure ... Read More

Database failure is a quite common problem of information technology. It can occur even with good database system software. There may be a simple error which can lead to loss of the complete database.Causes of database failureSome of the causes for database failure are as follows −Database file corruptionIf a file in the database is corrupted or damaged, it can lead to the database failure. The file can become corrupt due to the following reasons −Changes in the SQL Server account.Accidental data deletion.File header corruption.Errors in accessing the data.InterruptionWhen the server or computer is not shut down properly or during ... Read More