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Distributed Database Management System

Distributed Database Management System. Lecture 8. Semijoin. S =. R.  AB (S). F. R. F. Subset of tuples of R that participate in join of R with S. Division. The division of R with degree r with S with degree s is the set of (r-s)-tuples t such that.

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Distributed Database Management System

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  1. Distributed Database Management System Lecture 8

  2. Semijoin S = R AB (S) F R F • Subset of tuples of R that participate in join of R with S BZUPAGES.COM

  3. Division • The division of R with degree r with S with degree s is the set of (r-s)-tuples t such that BZUPAGES.COM

  4. RS = A(R)- A(A(R) xS)-R) for all s-tuples in , the tuple tu is in R. for all s-tuples in , the tuple tu is in R. BZUPAGES.COM

  5. R S The employees who work in all projects more than 10M budget BZUPAGES.COM

  6. Relational Calculus

  7. Rather than how to obtain results, we say what the result is by specifying relationship between data BZUPAGES.COM

  8. Tuple Relational Calculus • Based on first-order predicate logic • Expressed as { t | F(t)} • Where t is a tuple variable and F is well-formed formula BZUPAGES.COM

  9. Find the set of all tuples t such that F(t) is true, where F implies the predicate condition. BZUPAGES.COM

  10. Atomic Formula • Tuple-variable membership expression: specified as R(t) or R.t • Conditions • s[A] Θ t[B] • S[A] Θ c BZUPAGES.COM

  11. SQL • Language based on Tuple-oriented Calculs BZUPAGES.COM

  12. Example • Select EMP.eName, DEP.dName from EMP, DEP where EMP.dNo = DEP.dNo BZUPAGES.COM

  13. Domain Relational Calculus • Domain variable ranges over values in a domain and specifies a tuple BZUPAGES.COM

  14. A query in DRC x1,x2,….xn|F(x1,….xn) where F is a wff and Xs are free variables • Implementation: QBE • Query by Example (QBE) is a method of creating database queries using examples based on a text string, the name of a document or a list of documents. The QBE system converts the user input into a formal database query. This approach allows the user to perform powerful searches without the need of having to learn a more formalized query mechanism such as Structured Query Language (SQL). BZUPAGES.COM

  15. Interface with Programming Languages

  16. Tightly Coupled • Programming Language and database languages are merged • Loosely Coupled • PL is extended with special concepts BZUPAGES.COM

  17. Computer Networks

  18. A computer network is a system for communication between two or more computers BZUPAGES.COM

  19. Computers are • Interconnected • Autonomous • NWing involves • Hardware components • Software components BZUPAGES.COM

  20. Computers are called Nodes, sites, hosts, in general node or host is meant the hardware and site means hw+sw • Other equipment at nodes is also possible like Printers, Disks etc. • Equipment connected via links and channels, link is a physical thing where as channel is logical one BZUPAGES.COM

  21. Data Communication

  22. Comm links carry data in form of Digital or analog signals • Each channel has a certain capacity, that is capability of transmitting data over a certain time unit • This capacity is referred as bandwidth BZUPAGES.COM

  23. Data transmitted on analog links is to be Modulated which is done by changing three basic properties carrier signal • At the receiving end it has to be Demodulated • Modem is the device that performs this task BZUPAGES.COM

  24. Multiplexing is the technique that allows multiple signals to be transmitted over the same line simultaneously • Two types FDM, TDM BZUPAGES.COM

  25. Mode of Operation • Simplex: link operates in only one direction, like printers • Half Duplex: can transmit in both directions, but not simultaneously, link has to be “turned around” • Full Duplex: Simultaneously both ways BZUPAGES.COM

  26. Performance of a Communication System • Bandwidth • Mode of Operation • Software employed • Redundancies within message • Headers and trailers with the message BZUPAGES.COM

  27. Block Error Check Text Header • Source Address • Destination Address • Message Number • Packet Number • Acknowledgement • Control Information BZUPAGES.COM

  28. Types of Networks

  29. Classification Criteria • Interconnection Structure (Topology) • Transmission Mode • Geo. Distribution (Scale) BZUPAGES.COM

  30. Topology based Classification

  31. Star Central Control Node BZUPAGES.COM

  32. Star • All communication via a central node • Excessive load on the central node • Disadvantage is that if the central node fails all network goes down BZUPAGES.COM

  33. Ring Network Unidirectional Ring Ring Interface BZUPAGES.COM

  34. Ring Network • Computers connected with transmission media in the form of loop • Each station also serves as a repeater, it repeats the signal that it receives • Control is generally managed via a Token BZUPAGES.COM

  35. A token is circulated on the around the network, with certain bit pattern to indicate the network is free • Any site wanting to communicate grabs the token, sets it to busy and then sends the message • When communication is over, the site again sets token to free BP BZUPAGES.COM

  36. To improve the reliability a double loop topology has been proposed that lessens the chance of network failure in case of a single node breakage BZUPAGES.COM

  37. Bus Network BUS BZUPAGES.COM

  38. Bus Topology • Common channel used to transmit and receive data • Link control is performed as • CSMA • CSMA/CD • In addition, token can also be used BZUPAGES.COM

  39. CSMA/CD • Behave in CSMA, except that node keep listening to bus after even they have transmitted • The purpose is to detect if some collision has occurred • Collision occurs when multiple sites try to transmit at the same time BZUPAGES.COM

  40. When collision is detected, sites abort the transmissions, wait for an arbitrary time and re-transmit the message BZUPAGES.COM

  41. Meshed Network BZUPAGES.COM

  42. Meshed Network • Every computer connected with every other. • Gives maximum reliability, but is not practicable even for not a very large network BZUPAGES.COM

  43. Transmission Mode

  44. Point to Point (unicast) • Broadcast (multi-point networks) BZUPAGES.COM

  45. Point to Point • One or more links between sender and receiver • Link may be direct or via intermediate connections • Sender and receiver’s addresses are placed in the header of the message BZUPAGES.COM

  46. The intermediate nodes check the destination address in the message header, if not for them transmit to next intermediate node • Communication medium is generally Coaxial, Twisted Pair or the Fibre optic cables BZUPAGES.COM

  47. Broadcast Networks • Common channel utilized by all nodes • Message received by all, ownership checked • Multicasting: message sent to a certain subset of nodes in nw • Generally Radio or Satellite based BZUPAGES.COM

  48. In Satellite based, each site beams transmission to satellite • That beams it back at a different frequency • Broadcast Networks can also use Microwave that can be over Satellite or Terrestrial BZUPAGES.COM

  49. Scale

  50. Local Area NW • Metropolitan Area NW • Wide Area NW • Distinction between them is blurred, still they exist • Major categorization is probably Protocols, to be discussed next BZUPAGES.COM

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