Matakuliah
Tahun
Versi
: M0174/OBJECT ORIENTED DATABASE
: 2005
: 1/0
Pertemuan 15
Object Query Language (Lanjutan
bagian 2)
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Mahasiswa dapat Menghasilkan query
language dalam object data model (C3)
2
Outline Materi
• Processing mutable objects
• Processing a collection of many types of
object
• Computations on arithmetic and string
literal
3
Processing mutable objects
• Mutable objects are manipulated by
executing the operations defined for the
respective object types
• Example
4
Processing a collection of many types of object
• An added complexity can occur when
executing operations on a collection object
which contain objects of many types.
• In such situations, there may be multiple
implementations of the operation. It is
therefore necessary to determine, for each
object, which implementation to use
5
Processing a collection of many types of object
• OQL supports two different ways of
resolving this problem:
– Late binding: this mechanism allow general
query to be specialized for each object when
query is execute.
– Class indicator: class indicator override late
binding to ensure that only objects of a
specified type are accessed.
6
Processing a collection of many types of object
• Late binding is a useful mechanism, since
it allows operations to be invoked at the
most general level but then executed at
the most specific.
• This simplifies application programs, since
they don’t have to take into account
difference between subtypes
7
Processing a collection of many types of object
• Late binding also insulates applications
program from many change to the object
database.
• Sometime we may wish to override late
binding and ensure that we process only
specific types of object within a collection.
This done by Class Indicator, for example:
Select ((RetailCustomer) c).discount from
Customer c
8
Computations on arithmetic and string literal
• In addition to the user-defined operations
on objects, OQL includes a number of built
in operations upon literal
• These can be used to construct queries
which perform arithmetic computations on
numeric
• Example
9
Computations on arithmetic and string literal
<query> ::= <query> + <query>
| <query> - <query>
| <query> / <query>
| <query> * <query>
| - <query>
| <query> mod <query>
| abs <query>
10
SUMMARY
• Mutable objects can be processed by
executing instance operations
• These are accessed using paths
• When this is done, there is a danger of
side-effects
11
SUMMARY
• When collection contains many types of
object, the correct implementation of an
operation is chosen using late binding
• This can be overridden with class indicator
12