Relier Pairs Base de Datos Distribuidas P2Version en ligne Las descripciones más largas han sido recortadas para poder ingresarlas en este sistema pero se trato dejar lo más importante de cada descripción. par Mariana Ávila Rivera 1 Produces a horizontal subset of the operand relation (sF(R)={tR ard F(A) is true}) 2 Result of this operation contains all tuples that are in R, but not in S (R - S = {tIti Rand ti S}). 3 Result of this operation contains tuples that are in R or in S, but not both, duplicates are removed (RÈ S-{t| t Ror t S}) 4 Result of RxS is a relation of degree k1+k2 and consists of all(n1*n2)-tuples where each uple is a concatenation of one tuple of R with one tuple of S 5 Specify how to obtain the result using a set of operators and operands into relations. 6 This produces a vertical slice of a relation (PA1,.,An(R)=(#[A1,..., An] | AR}) Union Operation Set Difference Selection operation Projection operation Cartesian (Cross) Product operation Relational algebra 1 Includes tuples from one or both relations that don't meet the join condition, filling other relation's attributes with NULL. 2 Specify the properties that the result should hold. 3 SQL is an example of this relational calculus (at least in its simple form) 4 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 5 Query of the form x1,x2..,xnIF(x1,x2,..,xn) where F is a well-formed formula in which x1,x2..,xn are the free variables QBE is an example is a type of 6 An interconnected collection of autonomous computers that are capable of exchanging information among themselves Tuple relational calculus Relational Calculus Outer-Join Computer Network Domain relational calculus Natural join 1 Messages are sent over a shared channel and received by all nodes; each checks the address and ignores it if not the recipient — a trait of: 2 One or more (direct or indirect) links between each pair of nodes and communication always between two nodes are characteristics of 3 Long delays due to distance traveled, heterogeneity of transmission media and speeds of 150Mbps-10Gbps (OC192 on the backbone) are characteristics of 4 Star, Ring and Mesh are part of: 5 Hosts (nodes, end systems), Switches and Communication link, are: 6 Speeds 10-1000 Mbps, short delays and low noise and limited in geographic scope (usually< 2km) Broadcast scheme communication. Wide area network (WAN Network Components. Point-to-point (unicast) scheme communication. Types of networks topologies Local area network (LAN) 1 In this data communication form, a dedicated channel is established between the sender and receiver for the duration of the session 2 The amount of information that can be trnsmitted over the channel in a given time unit: 3 Twisted pair, coaxial and microwave are: 4 This software that ensures error-free, reliable and efficient communication between hosts. 5 In this data communication form, messages are divided into fixed size packets, each of which is routed from the source to the destination 6 Application, transport, Network and Individual networks are part of: Communication alternatives. TCP/IP Protocol. Communication protocol Capacity - bandwidth Circuit switching Packet switched 1 The placement of the distributed DBMS software; and placement of the applications that run on the database determinates: 2 Making decisions about the placement of data and programs across the sites of a computer network as well as possibly designing the network its 3 The quantity of information about how users access data are defines 4 Level of sharing, pattern behavior and level of knowledge are: 5 Static and dynamic alternatives are two types of: 6 Data sharing and data-plus program sharing determines Pattern behavior The placement of applications The three orthogonal dimensions of organization in DDBS Main problem of DDBS design The level of knowledge in DDBS The level of sharing in DDBS. 1 Requirement analysis, View design and Conceptual design are: 2 Goes from one extreme not fragment to the other extreme fragment to the level individual tuples (horizont. frag) or individual attributes (ver. frag) 3 This design method starts with a general idea of the system and gradually defines specific details of how it will interact 4 The latter, on the other hand, has unnecessary replication. These are reasons to: 5 These two DDBS design approaches seem very different but share the goal of uniting the system by describing all process interactions 6 The relation is either stored at one site or replicated at all/some application sites. The first causes high remote data access volume. 7 This design is presented when the databases already exist at several sites The degree of fragmentation Top-down design The first part of a framework for top-down design process. Fragment a DDB Top-down and Bottom-up design Fragment a DDB Bottom-up design 1 Fully replicated; each fragment at each site and partially replicated; each fragment at some of the sites are part of 2 Completeness, Reconstruction, and Disjointness are rules during fragmentation that ensure no semantic change, and are called: 3 Relation instances are tables, so the issue is finding ways to divide a table into smaller ones. There are two alternatives: 4 The logical database organization, application locations, access characteristics, and the properties of the computer system at each site are part of: 5 With proper fragmentation, one must choose how to allocate fragments across network sites, selecting among allocation alternatives of 6 A horizontal fragment Ri of relation R consists of all the tuples of R which satisfy a minterm predicate mi Dividing it horizontally or dividing it vertically. Primary Horizontal Fragmentation Replicated and non-replicated alternatives Information requirements to DDBS A replicated alternative Test correctness 1 It is the partitioning of a relation that results from predicates being defined on another relation 2 Splitting and grouping are two approaches of: 3 The frequency with which a user application qi accesses data. 4 It is performed using predicates that are defined on the original relation. 5 The number of tuples of the relation that would be accessed by a user query which is specified according to a given minterm predicate mi. 6 Set of simple predicates Pr is complete if accesses to tuples in minterm fragments require equal probability of access for tuples in the same fragment Completeness of Simple Predicates Derived Horizontal Fragmentation (DHF) Access frequencies Minterm selectivities Primary Horizontal Fragmentation (PHF) Vertical Fragmentation.
