DBMS
Drawing and Reading ER Diagrams
A complete guide to ER notation and a repeatable eight step method for turning a written requirement into a correct, readable ER diagram.
#Interview
Interview preparation material.
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DBMS
Strong and Weak Entities
A weak entity has no key of its own and can only be identified through an owner entity. It is drawn with a double rectangle, joined by an identifying...
DBMS
Cardinality and Participation Constraints
Cardinality says how many entities on one side may relate to entities on the other; participation says whether every entity must take part. Together t...
DBMS
Relationships, Relationship Sets and Degree
A relationship is an association among entities. Relationship types have a degree, may carry their own attributes, and may connect an entity type to i...
DBMS
Keys in the ER Model
A key attribute distinguishes one entity from another. Understanding super keys, candidate keys, primary keys and partial keys at design time prevents...
DBMS
Types of Attributes in the ER Model
Attributes are simple or composite, single valued or multivalued, stored or derived, and may be complex, key or null valued. Each type converts into t...
DBMS
Entities, Entity Sets and Entity Types
An entity is a distinguishable thing the database stores facts about, an entity type is its definition, and an entity set is the collection of entitie...
DBMS
Comparing Data Models and Choosing One
A single comparison of hierarchical, network, relational, object oriented, object relational and NoSQL models, plus a practical method for choosing a...
DBMS
Object Oriented and Object Relational Models
The object oriented model stores objects with identity, state and behaviour. The object relational model adds those ideas to a relational core, which...
DBMS
The Relational Model as a Data Model
The relational model stores everything in tables and connects them by matching values rather than pointers. That one decision delivers declarative que...
DBMS
Hierarchical and Network Data Models
The hierarchical model arranges records in a tree with one parent each; the network model allows many parents through a graph of sets. Both used physi...
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...