Database Joins, Network Types, and Distributed Design
Database Joins
A join is derived from the Cartesian product. There are various forms of joins:
0-JOIN
It is an equi-join of two relations R and S over an attribute (or attributes).
NATURAL JOIN
In an outer join, tuples exist in the result relation regardless.
OUTER JOIN
Defined over the set of attributes A, by relation S, defined over the set.
SEMIJOIN
Decreases the number of tuples that need to be handled to form the join.
Advantage of SEMIJOIN
RELATIONAL CALCULUS
Specifies the properties that the result should hold using Tuple relational calculus.
Network Types and Communication
TYPES OF NETWORKS
Irregular, Bus, Star, Ring, Mesh
COMMUNICATION SCHEMES
Point-to-point (unicast), Broadcast (multi-point)
POINT TO POINT
One or more (direct or indirect) links between each pair of nodes.
COMMUNICATION ALTERNATIVES
Twisted pair, Coaxial, Fiber optic cable, Satellite, Microwave, Wireless
COMMUNICATION PROTOCOLS
Software that ensures error-free, reliable, and efficient communication between hosts.
DIMENSIONS OF THE PROBLEM
Can be investigated along three orthogonal dimensions.
NO SHARING
Each application and its data execute at one site, and there is no communication.
DATA SHARING
All the programs are replicated at all sites, but data files are not. Accordingly, user requests…
STATIC
The user requests do not change over time (difficult to find in real apps).
DATA PLUS SHARING
Both data and programs may be shared, meaning that a program…
DYNAMIC
The user requests change over time more commonly in DDBS.
SECOND POSSIBILITY
Designers have complete information.
THIRD POSSIBILITY
Designers have partial information.
TOP DOWN
Mostly in designing systems from scratch.
REQUIREMENTS ANALYSIS
Defines the environment of the system and elicits both the data.
VIEW DESIGN
This activity deals with defining the interfaces for end users.
CONCEPTUAL DESIGN
This is the process by which the enterprise is examined to determine…
Distributed Database Design Issues
DIST. DESIGN ISSUES
We will enforce the following three rules during fragmentation, which, together…
COMPLETENESS
Decomposition of relation R into fragments R1, R2, …, Rn is complete.
RECONSTRUCTION
If relation R is decomposed into fragments R1, R2, …, Rn, then there should…
NON REPLICAT.
Each fragment resides at only one site.
REPLICATED
Each fragment at each site partially replicated: each fragment…
RULE OF THUMB
If read-only queries / update queries << 1, replication is advantageous.
PRIMARY HORIZONTAL FRAG
It is performed using predicates that are defined on the original relation.
DERIV HORIZONTAL FRAG
It is the partitioning of a relation that results from predicates being defined.
MINTERM SELECTIVITIES
The number of tuples of the relation that would be accessed by a user.
ACCESS FREQUENCYS
The frequency with which a user application qi accesses data.
If relation R is fragmented into FR = {R1,R2,…,Rr}.