Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Q. Explain data aggregation and discuss different design constraints.
Sol. Aggregation One limitation of the E-R model is that it cannot express relationships among relationships. To illustrate the need for such a construct consider the ternary relationships works on which we will see between a employee, branch and job (see figure). Now, suppose we want to record managers for tasks performed by an employee at a branch that is we want to record managers for (employee branch job) combinations. Let us assume that there is an entity set manager. One alternative for representing these relationships is to create a quaternary relationship manages between employee, branch, job and manager (A quaternary relationships required a binary relationship between manager and employee would not permit us to represent which (branch, job) combinations of an employee are managed by which manager.) Using the basic E R modeling constructs we obtain the E R diagram of given figure. It appears that the relationship sets works on and manages can be combined into one single relationship set. Nevertheless we should not combine them into a single relationship since some employee; branch job combinations may not have a manager. There is redundant information in the resultant figure however since every employee; branch job combination it manages is also in works on. If the managers were a value rather than manager entity we could instead make manager a multivalued attribute of the relationship works on. But doing so makes it more difficult to find for example employee branch job triples for which a manager is responsible. Since the manager is manager entity this alternative is ruled out in any case. The best way to model a situation such as the just described is to use aggregation. Aggregation is an abstraction through which relationship are treated as higher level entities. Thus for our example we regard the relationship set works on as a higher level entity set called works on. Such an entity set is treated in the same manager between works on and manager to represent who manages what tasks. Figure shows a notation for aggregation commonly used to represent the above situation.
I want an iPad app that is a simple 1 page form to complete with text. The Objective is to allow a few dozen people of the same organization (they're all on iPad) to open the app,
What is the archtetype/instance pattern? The archetype/instance pattern happens when one entity tracks occurrences of another entity. A common example is the relationship among
What is a Phantom Deadlock? In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to recognize deadlocks
Table Handling In RDBMS more than one table can be tackled at a time by using join operation. Join operation is a relational operation that causes 2 tables with a common domai
Birla Institute of Technology & Science, Pilani Work-Integrated Learning Programmes Division Second Semester 2012-2013 EC-1 Assignment 2 (7.5% of the grade) Course No. : SS ZG
List any eight applications of DBMS. a) Universities b) Airlines c) Banking d) Credit card transactions e) Tele communication f) Sales g)Finance h) Manufac
Explain Instance and schemas? Instances and schemas: Databases changes over time as the information is deleted and inserted. The collection of information stored in database
Explain the Cartesian product: The Cartesian product operation does not need relations to union-compatible. The meaning of this is that the involved relations may have dissim
Define Direct file organization? The direct file organization is employed to enhance the performance in accessing the records than sequential file organization. In direct file
Explain natural join? Natural Join - Similar as equi-join except in which the join attributes (having similar names) are not involved in the resulting relation. Only one sets
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd