1. Chapter 2 .Computational Models
Ha,Hong Pyo

2. Outline Paper information Introduction What is model?
Transaction Model
Conclusion

3. Introduction
Modeling in transaction in database

4. What is model? Definition That is descriptive statements for object
expressed in a given language

5. PURPOSE OF MODEL
SPECIFYING
IMPLEMENTATION MODEL
ABSTRACTION

6. Origin meaning of model
The term “model” is derived from the Latin word modulus,
which means measure, rule, pattern, example to be
followed. Obvious examples are toy railways and dolls,
maps, architectural models of buildings. In software engineering,
we have process models, design patterns, class
diagrams. Other models are less obvious, like project
plans, specifications and designs, metrics, and minutes of
project meetings.

7. How is a model used?
FROM SUS
DUDUCTION NEW STATEMENTS

8. What is a transaction? Definition of a transaction from user viewpoint
The execution of a program to perform a function (functions) by accessi ng a shared database, usually on behalf of a user (application)
You have a requirement (air ticket booking) -> Your system implements a function to meet your requirement -> You invoke the function to book an air ticket -> a transaction is created
Other Examples:
Reserve a room in a hotel
Withdraw money from an ATM
Verify a credit card sale
Update a student record
Place an order using an on-line catalog on the Internet

9. SIMPLE MODEL OF A DATABASE
A database - collection of named data items
Granularity of data - a field, a record , or a whole disk block (Concepts are independent of granularity)
Basic operations are read and write
read_item(X): Reads a database item named X into a program variable. To simplify our notation, we assume that the program variable is also named X.
write_item(X): Writes the value of program variable X into the database item named X.

10. Computational Models for transactional server
Defining elementary options on objects
Execution of transaction programs can be modeled
Obtaining schedules or histories as an abstract notion of concurrent execution
Identifying ACID properties
Creating correct algorithm and protocols

11. partial order’s Formal definition
A partial order is a binary relation "≤" over a set P which is reflexive, antisymmetric, and transitive, i.e., for all a, b, and c in P, we have that:
a ≤ a (reflexivity);
if a ≤ b and b ≤ a then a = b (antisymmetry);
if a ≤ b and b ≤ c then a ≤ c (transitivity).

12. Differences between Object model and page model
Elementary options
What kind of elementary operation ,we consider lead to the distinction page model and the object the model
Page model : these are pages with read and write operation
Object model : these are general objects with an encapsulated set of operations appllicable to them

13. Backup/Recovery Manager
Read/write model
We abstract from transaction semantics except for database reads and writes.
Basic operations in the model?
Basic operations must be guaranteed to be formal consistent, atomic and isolated.
Transaction 1
Transaction 2
...
Transaction n
Scheduler
restart
restore
Backup/Recovery Manager
Database Manager
Archive Manager
Database
We are only concerned with database consistency  we are only interested in database reads and writes.

14. Read/write model “Syntax”: (Read/Write Model Transaction):
A transaction t is a partial order of steps (actions) of the form r(x) or w(x), where x  D (D database) and reads and writes applied to the same object are strictly ordered.
We write t = (op, <)
for transaction t with step set op and partial order <.
Examples: t1 = r(s)w(s)r(v)w(v)
for short: r(s) w(s) r(v) w(v)
t2 = r(s)w(s)
r(v)w(v)

15. Read/write model Worst-case assumption! “Syntax”:
(Read/Write Model Transaction):
A transaction t is a partial order of steps (actions) of the form r(x) or w(x), where x  D (D database) and reads and writes applied to the same object are strictly ordered.
We write t = (op, <)
for transaction t with step set op and partial order <.
“Semantics”:
Interpretation of jth step, pj, of t:
If pj=r(x), then interpretation is assignment vj := x to local variable vj
If pj=w(x) then interpretation is assignment x := fj (vj1, ..., vjk).
with unknown function fj and j1, ..., jk denoting t‘s prior read steps.
Worst-case assumption!

16. Page model transaction
A transaction t is a partial order of steps(actions) of the form r(x) or w(x) , where x < D and reads and writes as well as multiple writes applied to the same data item are ordered. More formally, a transaction is pair
t = ( op, < )
The page model as described above allows a transaction to read or write the same data item more than once, as it the case in the example
t = r(x)w(x)r(y)r(x)w(x)

17. Object model transaction
A transaction t is a (finite) tree of labeled nodes with
The transaction identifier as the label of the root node
The names and parameters of invoked operations as labels of inner
Page model read/write operations as labe니 of leaf nodes

18. Database system internal layers
Person who lives in Austin
Inspecting result
SQL Command translated into operation at the query processing layer at compile time
Search operation on an index that returns the RID(address)

19. DISCUSSION , Q & A Session.
Does anybody have a question ?