1. Chapter 5
Other
Relational
Languages
By Cui, Can B.

2. The Languages
Query By Example (QBE) – Base on domain relational calculus.
Quel – Base on tuple relational calculus.
Datalog – modeled after the Prolog Language.

3. I. QBE: Introduction For Data Manipulation
1. It has two dimensional syntax, so it requires two dimensions for its expressions.
2. QBE queries are expressed “by example.”

4. QBE tables Users specify a query by filling in tables. Reserves sid
bid
day
Books
bid
btitle
type
Student
sid
sname
class
age

5. Basics Print names and ages of all students:
Sid
Sname
Class
age
P._N
P._A
Print all fields of students who are at least sophomores in ascending order by (class, age):
Student
Sid
Sname
Class
age P.
AO(1). > sophomore
AO(2).

6. Continue Print unique student names older than 25.
Names of student younger than 20 or older than 25:
Student
Sid
Sname
Class
age P.
>25
<20
Duplicates not eliminated by default:
Student
Sid
Sname
Class
age
UNQ P.
<25
Print unique student names older than 25.

7. Join Queries Print students who borrowed a book on 11/30/01.
Joins are accomplished by repeating variables
Student
Sid
Sname
Class
Age
_Id
P.S
Reserves
Sid
Bid
day
_Id
`11/30/01’
sid is the common attribute that join the two tables.
Print students who borrowed a book on 11/30/01.

8. Join Queries
Types of books reserved by students who have reserved a book for 11/30/01 and are older than 25.
Student
Sid
Sname
Class
age
_Id _S
>25
Reserves
Sid
Bid
day
_Id _B
`11/30/01’
Books
Bid
Bname
type _B P.

9. Aggregates QBE supports: AVG, COUNT, MIN, MAX, SUM
Student
Sid
Sname
Class
age
_Id G.
G.P.AO _A
P.AVG._A
G. are the group by fields – All tuples have the same values.
Unnamed columns – Print result of an expression.

10. Conditions Box Used to express conditions involving 2 or more columns.
Conditions can be expressed involving a group.
Student
Sid
Sname
Class
age P. _A
CONDITIONS
20 < _A AND _A <25
Print student names that are between the ages of 20 and 25.

11. Inserting & Deleting Tuples
Tuple insertion:
Student
Sid
Sname
Class
age I.
1369
Lisa
Senior 23
Tuple deletion: Delete all reservations for students with age<23
Student
Sid
Sname
Class
age
_Id
< 23
Reserves
Sid
Bid
day D.
_Id

12. II. Quel – Basic Structure
Range of t is r
- Declares t to be a tuple variable restricted to take on values of tuples in relation r.
Retrieve (t.attribute)
- The retrieve clause is similar in function
to the select clause of SQL.

13. Continue…
Where P
- The where clause contains the selection predicate.

14. Quel Query Structure Range of t is r Retrieve (t.A) Where P
Each t is a tuple variable.
Each r is a relation.
Each A is an attribute.
The notation t.A denotes the value of tuple variable t on attribute A.

15. Example Range of t is borrower Retrieve (t.CustomerName)
Find the names of all customers having a loan at the bank.
Range of t is borrower
Retrieve (t.CustomerName)

16. Example: Tuple Variables
Certain queries need 2 variables over
the same relation.
Example:
Find all customers who live in the same city as Smith.
Range of s is customer
Range of t is customer
Retrieve ( s.CustName )
Where t.CustName = “Smith and
s.CustCity = t.CustCity

17. Aggregate Function
Aggregate functions in Quel compute functions on groups of tuples.
An aggregate expression appear anywhere a constant may appear.

18. For Example In a where clause.
Find the average balance for all San Jose accounts.
Range of t is account
Retrieve avg (t.balance Where t.Branch = “San Jose”)

19. Modification of Database Deletion:
The form of a Quel deletion is:
range of t is r
delete t
where p
t can be implicitly defined.
Predicate P can be any valid Quel predicate.
If the where clause is omitted, all tuples
in the relation are deleted.

20. Example: Delete all of Lee’s account record: range of t is depositor
delete t
where t.CustName = “Lee”

21. Insertion append to account (branch = “San Jose” account = “123456”
Insertions are expressed in Quel using the append to.
Insert the account at the San Jose
branch with a balance of $ :
append to account (branch = “San Jose”
account = “123456”
balance = “5000”)

22. Updates Updates are expressed in Quel using the replace command
Increase all account balances by 5 percent:
range of t is account
replace t (balance = 1.05 * t.balance)

23. III. Datalog – Basic Structure
Logic based language that allows recursive queries.
A Datalog program consists of a set of rules that defines views.

24. Example:
Define a view relation vt containing account numbers and balances for accounts at the San Jose branch with a balance of over $100.
vt (A B) :- account ( “San Jose”, A B) B > 100
for all A,B
if (“San Jose”, A,B) E account A and B > 100
then (A,B) E vt

25. Datalog Rules A positive literal has the form: p(t1,t2,…,tn)
A negative literal has the form:
not p(t1,t2,…,tn)
p is the name of the relation with n attributes.
Each t is a constant or variable.

26. Continue… Rules are built out of literals and have the form:
p(t1,t2,…,tn) :- L1,L2…Ln
Each L is a literal
Head – the literal p(t1,t2,…,tn)
Body – the rest of the literals.

27. Semantics of a Rule
An instantiation rule is the result of replacing each variable in the rule by some constant.
Rule defining v1:
v1 (A,B):- account(“SanJose”, A,B), B>100
An instantiation Rule:
v1 (123456, 300) :- account (“San Jose”, “123456”,300) 300 > 100

28. Semantics of Recursion in Datalog
The view relations of a recursive program containing a set of rules K are defied to contain exactly the set of facts /.  facts / are derived from rules K.
Facts / is compute by a recursive procedure called Datalog-Fixpoint:
Procedure Datalog- Fixpoint
/ = set of facts in the database
repeat
Old./ = /
/ = / U infer (K,/)
until / = Old./
At the end of the procedure, infer ( K, / )= /
Datalog-Fixpoint will computes all the facts / until the rules in the program has all negative literal or no more true record according to the rules K.

29. QBE
QUEL
Datalog
THE END