GBD tema 1 inglés

The information independence implies: If the physical information model is modified then the logical information model must be accordingly modified. The logical information model modification does not necessarily imply modifying the physical information model. Any modification in a BBDD will necessarily imply the modification of the applications that her gain access. The information independence is established only between the physical and logical layer of the BBDD.

With regard to the variables in PL/SQL: They can be primitive type and of anchor type. Those of anchor type can be of the same type as a column of a table. Those of anchor type can store several lines of a table. Those of anchor type can store a only line of a cursor.

With regard to the stored procedures: It is a procedure that is executed in the DBMS. It is a procedure that is stored in the DBMS but it is executed in the client that invokes it. It is a procedure that is executed in the DBMS but it is stored in the client that invokes it. It allows to share code among different sessions.

Let the SQL sentece: INSERT X SET X.a=X.a+1. Let a trigger with the following header: “CREATE TRIGGER TRG_UPD_X_A AFTER INSERT FOR EACH ROW”: It will be executed once in any case. it will be executed once per updated line of the table X. It will not get access neither :new nor :old variables. It will get reading access to the table X.

Let the SQL sentece: UPDATE X SET X.a=X.a+1. Let a trigger with the following header: “CREATE TRIGGER TRG_UPD_X_A AFTER UPDATE FOR EACH ROW”: It will be executed once in any case. It will be executed once per updated line of the table X. It will not get access neither :new nor :old variables. It will get reading access to the table X.

Let the SQL sentece: UPDATE X SET X.a=X.a+1. Let a trigger with the following header: “CREATE TRIGGER TRG_UPD_X_A AFTER INSERT FOR EACH ROW”: It will be executed once in any case. It will be executed once per updated line of the table X. It will not get access neither :new nor :old variables. It will get reading access to the table X.

Let the SQL sentece: INSERT X SET X.a=X.a+1. Let a trigger with the following header: “CREATE TRIGGER TRG_UPD_X_A AFTER INSERT”: It will be executed once in any case. It will be executed once per updated line of the table X. It will not get access neither :new nor :old variables. It will get reading access to the table X.

Let the SQL sentece: UPDATE X SET X.a=X.a+1. Let a trigger with the following header: “CREATE TRIGGER TRG_UPD_X_A AFTER INSERT”: It will be executed once in any case. It will be executed once per updated line of the table X. It will not get access neither :new nor :old variables. It will get reading access to the table X.

A mutant table: It cannot be read by a row trigger. It cannot be modified by a row trigger. It can be read by a sentence trigger. It is a radioactive table.

The data dictionary: It is predefined by the DBMS, which keeps record of it. A user is able to make read-only operations. It describes, among other things, the logical model of information of the DDBB. It describes, among other things, the physical model of information of the DDBB.