BASE DE DATOS 2 Flashcards
APRENDER
Fundamental, Additional, Union compatibility
Relational Algebra Operators
Selection, Projection, Union, Set difference, Cartesian product
Fundamental
Intersection, 0-join, Natural join, Semijoin, Division
Additional
Produces a horizontal subset of the operand relation
(figura que parece una o con colita arriba) F(R)={t |tÎR and F(t) is true}
Selection
Produces a vertical slice of a relation
(figura que parece pi)A1,…,An
(R)={t[A1,…, An] | tÎR}
Projection
Similar to set unión
R U S={t | t Î R or t Î S}
Union
General Form
R – S = {t |t Î R and t Ï S}
Set Difference
R × S = {t [A1,…,Ak1
, Ak1+1,…,Ak1+k2
] | t[A1,…,Ak1
] Î R and
t[Ak1+1,…,Ak1+k2
] Î S}
Cartesian (Cross) Product
R (la figura de interseccion que parece una: n)S = {t | t Î R and t Î S}
= R – (R – S)
Intersection
is derivate of Cartesian product. There are various forms of join. The primary classification is between inner join and outer joi
0-Join
is derivate of Cartesian product. There are various forms of join. The primary classification is between inner join and outer joi
0-Join
The above example is a special case of 0-join which is called the equi-join.
Equi-join
It is a equi-join of two relations R and S over an attribute (or attributes) common to both R and S and projecting out one copy of those attributes
Natural join
Inner join requires the joined tuples from two operand relations to satisfy the join predicate. In contrast, in outer join tuples exist in the result relation regardless
Outer-Join
The tuples from the left operand relation are always in the result.
Left outer join
The tuples from the right operand relation are always in the result.
Right outer join.
Tuples from both relations are always in the result.
Full outer join
defined over the set of attributes A, by relation S, defined over the set of attributes B, is the subset of tuples of R that participate in the join of R with S
Semijoin
is that it decreases the number of tuples that need to be handled to form the join. It is important because it usually results in a decreased number of secondary storage access by making better use of memory.
The advantage of semijoin
Specify the properties that the result should hold Tuple relational calculus
Domain relational calculus
Relational Calculus
An interconnected collection of autonomous computers that are capable of exchanging information among themselves.
Computer Network
Irregular, Bus, Star, Ring, Mesh
Types of Networks
Point-to-point (unicast), Broadcast (multi-point)
Communication Schemes
One or more (direct or indirect) links between each pair of nodes
Communication always between two nodes
Receiver and sender are identified by their addresses included in the message header Message may follow one of many links between the sender and receiver using switching or routing
Point-to-point (unicast)
