1. CENG 352 Database Management Systems
Nihan Kesim Çiçekli
URL:

2. CENG 352 Database Management Systems
Instructor: Nihan Kesim Çiçekli
Office: A308
Lecture Hours: Tue. 10:40,11:40 (BMB1); Thu. 9:40 (BMB3)
Course Web page:
Teaching Assistant: Ömer Önder Tola
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CENG 352 Database Management Systems

3. Text Books and References
Raghu Ramakrishnan, Database Management Systems, McGraw Hill, 3rd edition, 2003 (text book).
R. Elmasri, S.B. Navathe, Fundamentals of Database Systems, 4th edition, Addison-Wesley, 2004.
A. Silberschatz, H.F. Korth, S. Sudarshan, Database System Concepts, McGraw Hill, 4th edition, 2002.
H. Garcia-Molina, J. D. Ullman, J. Widom, Database Systems The Complete Book, Prentice Hall, 2002.
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CENG 352 Database Management Systems

4. CENG 352 Database Management Systems
Grading
Midterm %
Assignments and Quizzes 20 %
Project %
Final Exam %
Exam Date:
Midterm Exam: 2nd week of April.
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5. CENG 352 Database Management Systems
Grading Policies
Policy on missed midterm:
no make-up exam
Lateness policy:
Late assignments are penalized up to 10% per day.
All assignments are to be your own work. Projects in groups of two.
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CENG 352 Database Management Systems

6. CENG 352 Database Management Systems
Course Outline
The Relational Data Model, Relational Algebra and Calculus, SQL
Query Evaluation and Optimization
Relational Database Design and Tuning
Transaction Management, Concurrency Control and Crash Recovery
Database Security and Authorization
Parallel and Distributed Databases
Object-Database Systems
Information Retrieval and XML Data
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7. CENG 352 Database Management Systems
Basic Definitions
Database: A collection of related data.
Data: Known facts that can be recorded and have an implicit meaning.
Mini-world: Some part of the real world about which data is stored in a database. For example, student grades and transcripts at a university.
Database Management System (DBMS): A software package/ system to facilitate the creation and maintenance of a computerized database.
Database System: The DBMS software together with the data itself. Sometimes, the applications are also included.
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8. Typical DBMS Functionality
Define a database : in terms of data types, structures and constraints
Construct or Load the Database on a secondary storage medium
Manipulating the database : querying, generating reports, insertions, deletions and modifications to its content
Concurrent Processing and Sharing by a set of users and programs – yet, keeping all data valid and consistent
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9. Typical DBMS Functionality
Other features:
Protection or Security measures to prevent unauthorized access
“Active” processing to take internal actions on data
Presentation and Visualization of data
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10. Example of a Database (with a Conceptual Data Model)
Mini-world for the example: Part of a UNIVERSITY environment.
Some mini-world entities:
STUDENTs
COURSEs
SECTIONs (of COURSEs)
(academic) DEPARTMENTs
INSTRUCTORs
Note: The above could be expressed in the ENTITY-RELATIONSHIP data model.
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11. Example of a Database (with a Conceptual Data Model)
Some mini-world relationships:
SECTIONs are of specific COURSEs
STUDENTs take SECTIONs
COURSEs have prerequisite COURSEs
INSTRUCTORs teach SECTIONs
COURSEs are offered by DEPARTMENTs
STUDENTs major in DEPARTMENTs
Note: The above could be expressed in the ENTITY-RELATIONSHIP data model.
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12. Example: Online Bookseller
Data = information on books (including categories, bestsellers, etc.), customers, pending orders, order histories, trends and preferences, etc.
Massive: many gigabytes at a minimum for medium-size bookseller, more if keep all order histories over all time, even more if keep images of book covers and sample pages
=> Far too big for memory
Persistent: data outlives programs that operate on it
Multi-user: many people/programs accessing same database, or even same data, simultaneously
=> Need careful controls
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13. CENG 352 Database Management Systems
Files vs. DBMS
Application must stage large datasets between main memory and secondary storage (e.g., buffering, page-oriented access, etc.)
Special code for different queries
Must protect data from inconsistency due to multiple concurrent users
Crash recovery
Security and access control
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14. What is a Relational Database?
Based on the relational model (tables):
acct # name balance
Sally
Sue
… … …
Today used in most DBMS's.
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15. CENG 352 Database Management Systems
Relational Model
Relational model is good for:
Large amounts of data —> simple operations
Navigate among small number of relations
Difficult Applications for relational model:
VLSI Design (CAD in general)
CASE
• Graphical Data
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16. CENG 352 Database Management Systems
Data Models
60’s
70's
80's
90’s
now
Hierarchical
Network
Relational
Choice for most new applications
Object Bases
Knowledge Bases
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17. CENG 352 Database Management Systems
The DBMS Marketplace
Relational DBMS companies – Oracle, Sybase – are among the largest software companies in the world.
IBM offers its relational DB2 system.
Microsoft offers SQL-Server, plus Microsoft Access for the cheap DBMS on the desktop, answered by “lite” systems from other competitors.
Relational companies also challenged by “object-oriented DB” companies.
But countered with “object-relational” systems, which retain the relational core while allowing type extension as in OO systems.
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18. Three Aspects to Studying DBMS's
1. Modeling and design of databases.
Allows exploration of issues before committing to an implementation.
2. Programming: queries and DB operations like update.
SQL = “intergalactic dataspeak.”
3. DBMS implementation.
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19. Database Schema vs. Database State
Database State (Instance): Refers to the content of a database at a moment in time.
Initial Database State: Refers to the database when it is loaded
Valid State: A state that satisfies the structure and constraints of the database.
Distinction
The database schema changes very infrequently. The database state changes every time the database is updated.
Schema is also called intension, whereas state is called extension.
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20. Three-Schema Architecture
Proposed to support DBMS characteristics of:
Program-data independence.
Support of multiple views of the data.
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21. Three-Schema Architecture
Many views (External schemas), single conceptual (logical) schema and physical schema(internal schema).
Views describe how users see the data.
Conceptual schema defines logical structure
Physical schema describes the files and indexes used.
View 1
View 2
View 3
Conceptual Schema
Physical Schema
Schemas are defined using DDL; data is modified/queried using DML.
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22. Three-Schema Architecture
Mappings among schema levels are needed to transform requests and data. Programs refer to an external schema, and are mapped by the DBMS to the internal schema for execution.
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23. CENG 352 Database Management Systems
Data Independence
Logical Data Independence: The capacity to change the conceptual schema without having to change the external schemas and their application programs.
Physical Data Independence: The capacity to change the internal schema without having to change the conceptual schema.
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24. CENG 352 Database Management Systems
Data Independence
When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS that fully supports data independence.
The higher-level schemas themselves are unchanged. Hence, the application programs need not be changed since they refer to the external schemas.
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25. CENG 352 Database Management Systems
Query Languages
Employee
Department
Name
Dept
Dept
Manager
SQL
SELECT Manager FROM Employee, Department WHERE Employee.name = "Clark Kent” AND Employee.Dept = Department.Dept
Query Language Data definition language (DDL) ~ like type definitions
Data Manipulation Language (DML) Query (SELECT) UPDATE < relation name > SET <attribute> = < new-value> WHERE <condition>
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26. CENG 352 Database Management Systems
Host Languages
C, C++, Java, Lisp, COBOL
Application prog.
DBMS
Calls to DB
Local Vars
(Memory)
(Storage)
Host language is completely general (Turing complete)
Query language—less general "non procedural" and optimizable
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27. CENG 352 Database Management Systems
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.
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28. Transaction: An Execution of a DB Program
Key concept is transaction, which is an atomic sequence of database actions (reads/writes).
Each transaction, executed completely, must leave the DB in a consistent state if DB is consistent when the transaction begins.
Users can specify some simple integrity constraints on the data, and the DBMS will enforce these constraints.
Beyond this, the DBMS does not really understand the semantics of the data. (e.g., it does not understand how the interest on a bank account is computed).
Thus, ensuring that a transaction (run alone) preserves consistency is ultimately the user’s responsibility!
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29. Scheduling Concurrent Transactions
DBMS ensures that execution of {T1, ... , Tn} is equivalent to some serial execution T1’ ... Tn’.
Before reading/writing an object, a transaction requests a lock on the object, and waits till the DBMS gives it the lock. All locks are released at the end of the transaction. (Strict 2PL locking protocol.)
Idea: If an action of Ti (say, writing X) affects Tj (which perhaps reads X), one of them, say Ti, will obtain the lock on X first and Tj is forced to wait until Ti completes; this effectively orders the transactions.
What if Tj already has a lock on Y and Ti later requests a lock on Y? (Deadlock!) Ti or Tj is aborted and restarted!
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30. CENG 352 Database Management Systems
Ensuring Atomicity
DBMS ensures atomicity (all-or-nothing property) even if system crashes in the middle of a Xact.
Idea: Keep a log (history) of all actions carried out by the DBMS while executing a set of Xacts:
Before a change is made to the database, the corresponding log entry is forced to a safe location. (WAL protocol; OS support for this is often inadequate.)
After a crash, the effects of partially executed transactions are undone using the log. (Thanks to WAL, if log entry wasn’t saved before the crash, corresponding change was not applied to database!)
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31. CENG 352 Database Management Systems
The Log
The following actions are recorded in the log:
Ti writes an object: The old value and the new value.
Log record must go to disk before the changed page!
Ti commits/aborts: A log record indicating this action.
Log records chained together by Xact id, so it’s easy to undo a specific Xact (e.g., to resolve a deadlock).
Log is often duplexed and archived on “stable” storage.
All log related activities (and in fact, all CC related activities such as lock/unlock, dealing with deadlocks etc.) are handled transparently by the DBMS.
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32. Structure of a DBMS A typical DBMS has a layered architecture.
These layers
must consider
concurrency
control and
recovery
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
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33. Centralized and Client-Server Architectures
Centralized DBMS: combines everything into single system including- DBMS software, hardware, application programs and user interface processing software.
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34. Basic Client-Server Architectures
The idea is to define specialized servers with specific functions.
File Servers
Printer Servers
Web Servers
Servers …
The client machines provide the user with the appropriate interfaces to utilize these servers, as well as with local processing power to run local applications.
All equipment is connected via a network.
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35. CENG 352 Database Management Systems
DBMS Server
DBMS server provides database query and transaction services to the clients
Sometimes called query and transaction servers
It is common that client and server software run on separate machines.
Two main types of basic DBMS architectures were created under this client/server framework:
Two-tier
Three-tier
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36. Two Tier Client-Server Architecture
User Interface Programs and Application Programs run on the client side
Interface called ODBC (Open Database Connectivity) provides an Application program interface (API) allow client side programs to call the DBMS. Most DBMS vendors provide ODBC drivers.
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37. Two Tier Client-Server Architecture
A client program may connect to several DBMSs.
Other variations of clients are possible:
e.g., in some DBMSs, more functionality is transferred to clients including data dictionary functions, optimization and recovery across multiple servers, etc.
In such situations the server may be called the Data Server (because it provides data in disk pages)
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38. Three Tier Client-Server Architecture
Common for Web applications
Intermediate Layer called Application Server or Web Server:
stores the web connectivity software and the rules and business logic (constraints) part of the application used to access the right amount of data from the database server
acts like a conduit for sending partially processed data between the database server and the client.
Additional Features- Security:
encrypt the data at the server before transmission
decrypt data at the client
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39. Classification of DBMSs
Based on the data model used:
Traditional: Relational, Network, Hierarchical.
Emerging: Object-oriented, Object-relational.
Other classifications:
Single-user (typically used with micro- computers) vs. multi-user (most DBMSs).
Centralized (uses a single computer with one database) vs. distributed (uses multiple computers, multiple databases)
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40. Classification of DBMSs
Distributed Database Systems have now come to be known as client server based database systems because they do not support a totally distributed environment, but rather a set of database servers supporting a set of clients.
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41. Variations of Distributed Environments:
Homogeneous DDBMS
Heterogeneous DDBMS
Federated or Multidatabase Systems
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42. 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!
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43. CENG 352 Database Management Systems
Summary
DBMS used to maintain, query large datasets.
Benefits include recovery from system crashes, concurrent access, quick application development, data integrity and security.
Levels of abstraction give data independence.
A DBMS typically has a layered architecture.
DBAs hold responsible jobs and are well-paid! 
DBMS R&D is one of the broadest, most exciting areas in CS.
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