Distributed Database Management System Data Model

Data Model

• A set of tools/ constructs used to model a database
• Record/Semantic

Legacy Data Models

• Hierarchical
• Network
• Relational

Relational Data Model

• Two major Strengths
• Three Components
• Relational databases based on relational Data Model
• A relation R defined over domains D₁, D₂, …., D_n is a set of n-tuples, <d₁, d₂, …, d_n> such that <d1 D₁……, d_nD_n

Schemes in RDB

• EMP(eNo, eName, eTitle, eSal, pNo, eResp, pDur)
• PROJ(pNo, pName, bud)
• Each of the attribute in these two relations has a domain, like…
• Domains need not to be distinct

Keys

Primary Key

• Minimum nonempty subset of a relation whose values uniquely identify each tuple in relation
• The superset of the key is super key, like…
• We also have candidate, alternate, secondary, foreign

Table

• Relation represented in a two dimensional form

EMP

PROJ

• After defining a relation’s scheme, it is populated
• Tuples are rows and attributes are cols
• Attributes get values from same domain
• Can have NULL value, but….

Normalization

• Step-by-step reversible process to produce anomalies free smarter tables
• Anomalies Types….
• Major step is decomposition
• Universal Relation approach
• Three Normal Forms
• BCNF
• Lossless decomposition
• Dependency preservation

Dependency Structure

• Norm. based on dependencies
• Up to BCNF on FDs
• MVD and P-JD

Dependencies

• A relation R defined on attributes A(A1, A2, …., An), if XA, YA, if for each value of X
• There is a unique value in Y, then X functionally determines Y, X Y
• If X Y and there is a Z X and Z Y, then X partially determines Y or Y is partially dependent on X
• A relation R defined on attributes A(A1, A2, …., An), if X A, Y A, Z A, if for each value of X
• There is unique value of (Y,Z) pair and Z depends only on X then X multi determines Z, X Z

P-J Dependency

• A relation R defined on attributes A(A1, A2, …., An), if X A, Y A, Z A, if R is equal to join of X, Y and Z then (X, Y, Z) constitute project-join dependency for R
• 1NF, attributes have only atomic values
• 2NF, there are no partial dependencies
• 3NF, for each X Y where Y is not in X, either X is a superkey of R or Y is prime attribute