CPS 510 Topic 4 Questions With Explained Correct Answers

A relational model uses - Correct Answers table (called relation) to represent a collection of related data values Rows are called __. - Correct Answers tuples columns are called __. - Correct Answersattributes *The number of attributes (i.e., number of columns) is called __. - Correct Answersdegree (also called arity) The data type describing the type of values that can appear in each column is called a __. - Correct Answersdomain A domain is a set of __ values - Correct Answersatomic Each value is __ as far as the relational model is concerned - Correct Answersindivisible tuples in a relation do not have any particular order. T or F - Correct AnswersTrue, theoretically, In practice, relations are stored as files. There is no order among the records T or F - Correct AnswersFalse Since we give names to columns, this ordering of values is not important T or F - Correct AnswersTrue When a relation is implemented as a file, the attributes are __. - Correct Answersordered A relation schema R of degree n is represented as - Correct AnswersR(A1, A2, . . ., An) An n-tuple t in a relation r(R) is denoted by - Correct Answerst = V1, V2, . . . , Vn » where Vi = attribute Ai »t[Ai] refers to the value of Vi in t »t[Au, Av, . . ., Az] refers to the subtuple of values Vu, Vv, . . ., Vz in t Q, R, S represent - Correct Answersrelation names q, r, s represent - Correct Answersrelation instances t, u, v - Correct Answersrepresent tuples Each entity in an entity type needs to be __. - Correct Answersidentified uniquely One or more attributes can be used as an entity identifier, T or F - Correct AnswersT For marks entity type, __ and __ are required to find the grade - Correct Answersstudent#, course# A superkey - Correct Answersis a key attribute + other attributes of relation examples: student#, SIN if we say in SQL: CREATE TABLE T ... ; T here is not a table. T or F - Correct AnswersF because it is a relation (table) variable whose values are relations (tables). Relations are __. - Correct Answersvalues; they can thus be "read" but not updated, by definition. You can't update any value, T or F - Correct AnswersT Relvars are - Correct Answersvariables; they can thus be "read" and updated, by definition. which system component determines how to implement user request? - Correct AnswersThe optimizer Optimizer has to do some "smart thinking" in order to support __. - Correct Answersautomatic navigation; when relational systems are responsible for locating a desired data a simple search for a tuple (record) optimizer can do simple sequential search or use index (if there is an index) is an example of using what system component? - Correct Answersoptimizer Catalog in a relational system will itself consist of ________. - Correct Answersrelvars (variables) The catalog is a set of... - Correct Answerssystem relvars. the purpose of a Catalog in a relational system - Correct Answersis to contain descriptors regarding the various objects that are of interest to the system itself, such as base relvars, views, indexes, users, integrity constraints, security constraints, and so on. How can a transaction terminate? - Correct AnswersNormally or Abnormally What is a transaction? - Correct Answersis a logical unit of work involving several operations that begins and terminates How does a Transaction begin? - Correct Answersbegins by BEGIN TRANSACTION Atomicity of a transaction - Correct Answerstransactions are guaranteed either to execute in their entirety or not to execute at all, even if the system fails halfway through the process. Durability of a transaction - Correct Answersonce a transaction successfully commits, its updates are guaranteed to be applied to the database, even if the system subsequently fails at any point. Isolation of a transaction - Correct Answersdatabase updates made by a given transaction T1 are kept hidden from all distinct transactions T2 until and unless T1 successfully commits. Serializability of a transaction - Correct Answersthe interleaved execution of a set of concurrent transactions is guaranteed to produce the same result as executing those same transactions one at a time in some (unspecified) serial order. Commit (normal termination) - Correct Answersoperation that signals successful end-of-transaction. Any updates made to the database by the transaction in question are now "made permanent" and become visible to other transactions. Rollback (abnormal termination) - Correct Answersis the operation that signals unsuccessful end-of-transaction. Any updates made to the database by the transaction in question are "rolled back" (undone) and are never made visible to other transactions