PENGANTAR MANAJEMEN BASIS DATA

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Pengenalan Database

Konsep dasar database, DBMS •  Basis data menyediakan fasilitas atau

mempermudah dalam menghasilkan informasi yang digunakan oleh pemakai untuk mendukung pengambilan keputusan

•  contoh penggunaan Aplikasi basis data dalam dunia bisnis : ……?

Sistem Pemrosesan Berkas Tradisional

•  Bentuk pemrosesan dasar yang lahir sebelum database muncul

•  Berkecunderungan tidak berbagi berkas (Setiap aplikasi memiliki berkas tersendiri)

Aplikasi Personalia Personalia

Aplikasi Pelatihan Pelatihan

Kelemahannya dari sistem pemrosesan berkas tradisional

1. Timbulnya data rangkap (redundancy data) dan Ketidakkonsistensi data (Inconsistency data)

2. Kesukaran dalam Mengakses Data

3. Data terisolir (Isolation Data)

4. Masalah Pengamanan ( Security Problem )

5. Data Dependence

Sistem Basis data •  Seiring dengan berjalannya waktu, lambat

laun sistem pemrosesan file mulai dit inggalkan karena masih bersifat manual, yang kemudian dikembangkanlah sistem pemrosesan dengan pendekatan basis data.

GAMBAR MENJADI SPT APA?

Definisi Database

•  “a collection of related data” (Elmazri & Navathe, 1994)

•  “an organized collection of logically related data” (McFadden, Hoffer, and Presscot, 2002)

•  “a collection of data, typically describing the activities of one or more related organizations” (Ramakrishnan & Gerke, 2000)

Data dan Basis Data •  Data adalah representasi fakta dunia nyata

yang mewakili suatu objek seperti manusia (pegawai, mahasiswa, pembeli), barang, hewan, peristiwa, konsep, keadaan, dan sebagainya yang direkam dalam bentu angka, huruf, simbol, teks, gambar, bunyi atau kombinasinya.

•  Basis Data adalah sekumpulan data yang terintegrasi yang diorganisasikan untuk memenuhi kebutuhan para pemakai di dalam suatu organisasi.

•  DBMS (Database Management System) adalah Perangkat Lunak yang menangani semua pengaksesan ke basis data

•  Sistem Basis Data terdiri dari basis data dan DBMS

Istilah - Istilah Dasar Basis Data •  Enterprise

• Bentuk organisasi :………? • Data operasional : ……….?

•  Entitas •  Contoh Entitas

•  Atribut (Elemen Data) •  Nilai Data (Data Value) •  Kunci Elemen Data (Key Data Element) •  Record Data

Pengguna Basis Data •  1. System Engineer •  2. Database Administrator (DBA) •  3. End User (Pemakai Akhir)

– a. Programmer aplikasi – b. Pemakai Mahir (Casual User) – c. Pemakai Umum (End User / Naïve User) – d. Pemakai Khusus (Specialized/

Sophisticated User)

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DBA SKILLS

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Levels of Abstraction •  Many views, single

conceptual (logical) schema and physical schema.

–  Views describe how users see the data.

–  Conceptual schema defines logical structure

–  Physical schema describes the files and indexes used.

☛  Schemas are defined using DDL; data is modified/queried using DML.

Physical Schema

Conceptual Schema

View 1 View 2 View 3

Example: University Database •  Conceptual schema:

–  Students(sid: string, name: string, login: string, age: integer, gpa:real)

–  Courses(cid: string, cname:string, credits:integer) –  Enrolled(sid:string, cid:string, grade:string)

•  Physical schema: –  Relations stored as unordered files. –  Index on first column of Students.

•  External Schema (View): –  Course_info(cid:string,enrollment:integer)

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DBMS  (Database  Management  System)

Application Programs Queries Database Schema

DML Preprocessor Query Processor DDL Compiler

Programs Object Code Database Manager Dictionary Manager

Access Method

File Manager

System Buffer

Database  dan  Data  Dic4onary

Komponen DBMS

Contoh-contoh Basis Data

Relasional : •  DB2 à IBM

•  ORACLE à Oracle •  SYBASE à Powersoft •  INFORMIX à Informix •  Microsoft Access à Microsoft •  MySQL

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Concurrency Control •  Concurrent execution of user programs is essential

for good DBMS performance. –  Because disk accesses are frequent, and

relatively slow, it is important to keep the cpu humming by working on several user programs concurrently.

•  Interleaving actions of different user programs can lead to inconsistency: e.g., check is cleared while account balance is being computed.

•  DBMS ensures such problems don’t arise: users can pretend they are using a single-user system.

Concurrency Control •  Concurrency control ensures that one

user’s work does not inappropriately influence another user’s work – No single concurrency control technique is

ideal for all circumstances – Trade-offs need to be made between level of

protection and throughput

Atomic Transactions •  A transaction, or logical unit of work (LUW), is a

series of actions taken against the database that occurs as an atomic unit – Either all actions in a transaction occur or

none of them do

Example: Atomic Transaction

Example: Atomic Transaction

Concurrent Transaction •  Concurrent transactions refer to two or more

transactions that appear to users as they are being processed against a database at the same time

•  In reality, CPU can execute only one instruction at a time – Transactions are interleaved meaning that the

operating system quickly switches CPU services among tasks so that some portion of each of them is carried out in a given interval

•  Concurrency problems: lost update and inconsistent reads

Example: Concurrent Transactions

Example: Lost Update Problem

Resource Locking •  Resource locking prevents multiple applications

from obtaining copies of the same record when the record is about to be changed

Lock Terminology •  Implicit locks are locks placed by the DBMS •  Explicit locks are issued by the application program •  Lock granularity refers to size of a locked resource

–  Rows, page, table, and database level –  Large granularity is easy to manage but frequently

causes conflicts •  Types of lock

–  An exclusive lock prohibits other users from reading the locked resource

–  A shared lock allows other users to read the locked resource, but they cannot update it

Example: Explicit Locks

Deadlock •  Deadlock, or the deadly embrace, occurs

when two transactions are each waiting on a resource that the other transaction holds

Example: Deadlock

Deadlock •  Preventing deadlock

– Allow users to issue all lock requests at one time – Require all application programs to lock

resources in the same order •  Breaking deadlock

– Almost every DBMS has algorithms for detecting deadlock

– When deadlock occurs, DBMS aborts one of the transactions and rollbacks partially completed work

Declaring Lock Characteristics •  Most application programs do not explicitly declare

locks due to its complication •  Instead, they mark transaction boundaries and

declare locking behavior they want the DBMS to use – Transaction boundary markers: BEGIN, COMMIT,

and ROLLBACK TRANSACTION •  Advantage

–  If the locking behavior needs to be changed, only the lock declaration need be changed, not the application program

Example: Marking Transaction Boundaries

Database Security •  Database security ensures that only

authorized users can perform authorized activities at authorized times

•  Developing database security – Determine users’ processing rights and

responsibilities – Enforce security requirements using security

features from both DBMS and application programs

DBMS Security •  DBMS products provide security facilities •  They limit certain actions on certain objects to

certain users or groups •  Almost all DBMS products use some form of

user name and password security

DBMS Security Model

DBMS Security Guidelines •  Run DBMS behind a firewall, but plan as though the firewall has been

breached •  Apply the latest operating system and DBMS service packs and fixes •  Use the least functionality possible

–  Support the fewest network protocols possible –  Delete unnecessary or unused system stored procedures –  Disable default logins and guest users, if possible –  Unless required, never allow all users to log on to the DBMS interactively

•  Protect the computer that runs the DBMS –  No user allowed to work at the computer that runs the DBMS –  DBMS computer physically secured behind locked doors –  Access to the room containing the DBMS computer should be recorded in

a log

DBMS Security Guidelines (cont.) •  Manage accounts and passwords

–  Use a low privilege user account for the DBMS service –  Protect database accounts with strong passwords –  Monitor failed login attempts –  Frequently check group and role memberships –  Audit accounts with null passwords –  Assign accounts the lowest privileges possible –  Limit DBA account privileges

•  Planning –  Develop a security plan for preventing and detecting security

problems –  Create procedures for security emergencies and practice them

Application Security

•  If DBMS security features are inadequate, additional security code could be written in application program –  Application security in Internet applications is often provided on the

Web server computer •  However, you should use the DBMS security features first

–  The closer the security enforcement is to the data, the less chance there is for infiltration

–  DBMS security features are faster, cheaper, and probably result in higher quality results than developing your own

Database Recovery •  In the event of system failure, that

database must be restored to a usable state as soon as possible

•  Two recovery techniques: – Recovery via reprocessing – Recovery via rollback/rollforward

Recovery via Reprocessing •  Recovery via reprocessing: the database

goes back to a known point (database save) and reprocesses the workload from there (re-execute all database update programs)

•  Unfeasible strategy because – The recovered system may never catch up if

the computer is heavily scheduled – Asynchronous events, although concurrent

transactions, may cause different results

Rollback/Rollforward •  Recovery via rollback/rollforward:

– Periodically save the database and keep a database change log since the save • Database log contains records of the data

changes in chronological order •  When there is a failure, either rollback or rollforward

is applied – Rollback: undo the erroneous changes made to

the database and reprocess valid transactions – Rollforward: restored database using saved data

and valid transactions since the last save

Example: Rollback •  Before-images: a copy of every

database record (or page) before it was changed

Example: Rollforward •  After-images: a copy of every database

record (or page) after it was changed

Example: Transaction Log

Checkpoint •  A checkpoint is a point of synchronization between the

database and the transaction log – DBMS refuses new requests, finishes processing

outstanding requests, and writes its buffers to disk – The DBMS waits until the writing is successfully

completed à the log and the database are synchronized

•  Checkpoints speed up database recovery process – Database can be recovered using after-images

since the last checkpoint – Checkpoint can be done several times per hour

•  Most DBMS products automatically checkpoint themselves

Overview of System Architecture

Database Cache

Log Buffer

Stable Database

Stable Log

Database Page

Database Page

Log Entry

Log Entry

read

write

begin

commit, rollback

write

fetch flush force Volatile Memory Stable

Storage

Database Server

Databases make these folks happy ...

•  End users and DBMS vendors •  DB application programmers

–  E.g. smart webmasters •  Database administrator (DBA)

–  Designs logical /physical schemas –  Handles security and authorization –  Data availability, crash recovery –  Database tuning as needs evolve

Must understand how a DBMS works!

Structure of a DBMS

•  A typical DBMS has a layered architecture.

•  The figure does not show the concurrency control and recovery components.

•  This is one of several possible architectures; each system has its own variations.

Query Optimization and Execution

Relational Operators

Files and Access Methods

Buffer Management

Disk Space Management

DB

These layers must consider concurrency control and recovery

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TUGAS 1.  Tugas per kelompok, 1 kelompok : …mhs 2.  Per kelompok tentukan contoh kasus

suatu sistem informasi atau aplikasi bebas yang digunakan pada satu organisasi. Misal : Aplikasi ATM

Contoh kasus tidak harus seluruh sistem atau aplikasi, satu subsistem atau satu modul saja.

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3. Dari contoh kasus yang sudah ditentukan b u a t R a n c a n g a n D a t a b a s e d a n Implementasi nya secara sederhana. Rancangan database dapat menggunakan alat bantu ERD atau Class Diagram 4. Aplikasi sederhana, buat tampilan input dan output yang merepresentasi rancangan database yang telah dibuat. 56

Contoh : •  Aplikasi ATM untuk Modul Informasi Saldo •  Rancangan Database

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•  Form Input

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•  OUTPUT

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Nomor Rekening : …. Nama : …. Saldo : X.XXX.XXX

FORMAT PRESENTASI •  NAMA SISTEM INFORMASI •  GAMBARAN UMUM SISTEM INFORMASI •  SUB SISTEM •  RANCANGAN DATABASE •  APLIKASI SEDERHANA à LANGSUNG

KE PROGRAM –  INPUT – OUTPUT

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