DBMS
Relation Schema and Relation Instance
A relation schema is the fixed definition of a relation; a relation instance is the set of tuples in it right now. A relational database schema is the...
#Database Concepts
Core ideas every database course begins with.
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DBMS
What a Data Model Is
A data model is the set of concepts used to describe data, relationships, semantics and constraints. Models are grouped as high level, representationa...
DBMS
Client Server Architecture and Database Servers
In client server architecture the database server owns the data and answers requests, while clients ask questions. Understanding what the server keeps...
DBMS
One Tier, Two Tier and Three Tier Architecture
Tier architecture describes how many machines or layers a database request passes through. One tier is local, two tier puts the application on the cli...
DBMS
Database Applications and the Database System Environment
Where databases are actually used, and what sits inside a running database system: the DBMS software, the stored database, the catalog, the applicatio...
DBMS
Schema, Instance and Metadata
A schema is the design of a database and rarely changes. An instance is the data in it at one moment and changes constantly. Metadata is the stored de...
DBMS
Logical and Physical Data Independence
Data independence is the ability to change a schema at one level without changing the level above. Physical independence is easy to achieve; logical i...
DBMS
Three Level Architecture and Data Abstraction
The ANSI-SPARC architecture separates a database into external, conceptual and internal levels. That separation is what makes data abstraction and dat...
DBMS
Advantages and Limitations of a DBMS
A DBMS buys controlled redundancy, enforced integrity, sharing, security, recovery and independence. It charges for them in cost, complexity, hardware...
DBMS
File System versus DBMS
The file based approach fails on redundancy, inconsistency, isolation, atomicity, concurrency, security and integrity. Each failure maps to one specif...
DBMS
What a DBMS Is and Why It Exists
A DBMS is the software layer between users and stored data. It exists to give many users controlled, concurrent, recoverable and consistent access to...
DBMS
Data, Information and Databases
Data is raw recorded fact, information is data placed in context, and a database is an organised, shared, self describing collection of related data...