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.
Define lock? Lock is the most common used to execute the requirement is to permit a transaction to access a data item only if it is currently holding a lock on that item.
Define Catalog and meta data ? A catalog is a compilation of records elaborating the contents of a particular collection or group of collections. Metadata (Meta data, or someti
What are the different kinds of database end users? Discuss the major activities of each? End-Users - End-users are the people whose jobs need access to the database for que
Describe Object Relational model ? Object Relational Model - This model combines the characteristics of both relational model and object oriented model. It extends the tradit
what are the type of the database
What is Secondary Index While making the index, generally the index table is kept in the primary memory (RAM) and the main table, because of its size is keeps in the secondary
10A.53 Code an Oracle Database trigger to enforce the constraint that an employee can never change his or her department. 10A.54 Code an Oracle Database trigger to allow the
for the following business rules . Identify all entities, attributes, relationships, primary keys, cardinalities and constraints where appropriate 3. (9) An art museum owns a larg
I want a professional with strong IT background who provide me timely assignments Project Description: I want a professional who can do my assignments for my major i.e. Infor
I want Database Of United Kingdom with Criteria of:\r\n\r\n1). Name, Number, City, State, Postal Code, Address, Email id, DOB.\r\n\r\n2). Unsecure Debts only adds Credit Card Payme
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