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DBMS Articles
Found 270 articles
Construct an ER diagram for a company in DBMS?
An Entity-Relationship (ER) diagram is a visual representation of the data model for a database. It shows entities, their attributes, and the relationships between them. In this article, we construct an ER diagram for a company database step by step. Problem Draw an ER model for a company considering the following constraints − In a company, an employee works on many projects which are controlled by one department. One employee supervises many employees. An employee has one or more dependents. One employee manages one department. Solution ...
Read MoreComponents of Storage Area Network (SAN)
Storage Area Network (SAN) is a dedicated, high-speed network that provides block-level data storage access to multiple servers from a centralized pool of storage devices. Unlike traditional direct-attached storage, SAN creates a separate network infrastructure specifically for storage traffic. The primary purpose of SAN is to enable data transmission between servers and storage devices, as well as facilitate data transfer between different storage systems. This architecture allows organizations to consolidate storage resources and provide scalable, high-performance storage access to multiple servers simultaneously. Storage Area Network Architecture ...
Read MoreOn Line Transaction Processing (OLTP) System in DBMS
OLTP (On-Line Transaction Processing) systems manage real-time transaction tasks − entering, storing, and retrieving data for daily operations like purchasing, payroll, and accounting. Examples include supermarket POS systems, order entry, retail sales, and financial transaction systems. Users POS, Web, App OLTP System INSERT, UPDATE DELETE, SELECT ...
Read MoreOLAP Operations in DBMS
OLAP (Online Analytical Processing) enables users to perform multidimensional analysis on data organized into cubes (hypercubes). Each cell in a cube corresponds to a specific combination of dimension values (e.g., Location → Time → Product). OLAP uses pre-aggregation and indexing for fast querying. Types of OLAP Servers Type Storage Trade-off ROLAP Relational database (SQL queries) Handles large data, slower queries MOLAP Multidimensional arrays Fast queries, limited data size HOLAP Hybrid (ROLAP + MOLAP) Scalability + speed balance OLAP Operations ...
Read MoreObject-Relational Features_ Object Database Extensions to SQL
The object-relational model combines relational databases with object database features. SQL (starting from SQL:1999 and refined in SQL:2008) incorporates object extensions including user-defined types, object identity, encapsulation, and inheritance. Key Object Features in SQL Feature Description Type Constructors ROW type (struct), ARRAY, SET, LIST, BAG for complex objects Object Identity REF types provide unique object identifiers (OIDs) Encapsulation Methods defined within UDTs (User-Defined Types) Inheritance UNDER keyword for type and table inheritance User-Defined Types (UDTs) UDTs allow creating complex-structured objects with custom attributes and ...
Read MoreObject Database Conceptual Design
An object database stores data as objects (containing both data and methods), working directly with object-oriented programming languages like Java and Python. Object-oriented modeling supports inheritance, encapsulation, and polymorphism, making it more flexible than the traditional relational model for complex relationships. ODB vs RDB Conceptual Design Feature Object Database (ODB) Relational Database (RDB) Relationships OID references (single or collections) Matching attribute values (foreign keys) Inheritance Built-in (extends, derives) No built-in construct Operations Part of class definition, specified early Can be delayed to implementation Multivalued Attributes Supported (set, bag, ...
Read MoreNumber of Possible Super Keys in DBMS
A super key is a set of one or more attributes that uniquely identifies each record in a table. All primary/candidate keys are super keys, but not all super keys are candidate keys (candidate keys are minimal super keys with no redundant attributes). Key Formulas Scenario (n = total attributes) Formula One candidate key with k attributes 2(n−k) Maximum super keys (at least 1 attribute) 2n − 1 Two candidate keys (Inclusion-Exclusion) SK(A1) + SK(A2) − SK(A1 ∪ A2) Three candidate keys SK(A1) + SK(A2) + SK(A3) − ...
Read MoreNode in Apache Cassandra
Apache Cassandra is an open-source NoSQL database written in Java, designed for high availability with no single point of failure. Nodes are the fundamental building blocks of Cassandra's distributed architecture, forming a peer-to-peer ring structure. Node in Cassandra Each node holds actual data along with metadata (location, data center, keyspaces, tables, schema). Nodes form a ring where every node is equal − no master/slave hierarchy. Data is distributed across nodes using a partitioner, and replicas are stored on multiple nodes for fault tolerance. ...
Read MoreNO-UNDO REDO Recovery Based on Deferred Update
In deferred update recovery, actual database modifications on disk are postponed until a transaction commits. Updates are recorded only in the log and cache buffers during execution. If a transaction fails before commit, the database on disk remains unaffected − hence NO-UNDO. Only REDO is needed for committed transactions whose changes haven't been written to disk. Deferred Update Protocol A transaction cannot modify the database on disk until it reaches its commit point. All REDO log entries must be force-written to disk before commit (Write-Ahead Logging). Only REDO log entries (new values/AFIM) are needed − no UNDO ...
Read MoreNetwork Attached Storage in DBMS
Network Attached Storage (NAS) is a dedicated storage device connected to a network that allows multiple clients to store and access files. In DBMS, NAS serves as a storage solution for database files, backups, and shared data without requiring a full server. NAS Storage Device LAN (Ethernet) DB Server Web Server ...
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