Looking at the data that happens to be stored in the tables for a particular application at some particular time, explain whether or not you can tell
a. What the key constraints for the tables are
b. Whether or not a particular attribute forms a key for a particular table
c. What the integrity constraints for the application are
d. Whether or not a particular set of integrity constraints is satis?ed
a. No, in one particular instance of the table, a particular attribute might uniquely identify the rows (and thus appear to be a key), but in other instances it might not.
b. You cannot tell whether a particular attribute is a key (for the reasons mentioned in (a)), but you can sometimes tell that a particular attribute cannot form a key by itself (if two distinct rows have the same value over that attribute).
c. No. Again, one cannot determine integrity constraints just by looking at database instances.
d. Yes. Simply check if every constraint in the set is satis?ed in the given instance.
You might also like to view...
Which of the following does NOT provide a live preview option??
A. ?Extra large icons B. ?Large icons C. ?Medium icons D. ?Small icons
Setting up a grid decreases the size and complexity of the Hypertext Markup Language (HTML) code by adding another level of markup.
Answer the following statement true (T) or false (F)
If you want to go up a single directory level, you can type cd followed immediately by _______________.
Fill in the blank(s) with the appropriate word(s).
A Windows Internet Name Service (WINS) server resolves fully qualified domain names and host names to IP addresses.
Answer the following statement true (T) or false (F)