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Introduction to Database Management Systems

Learn about the basics of database management systems, including data models, schemas, and query languages. Understand why DBMS is essential for efficiently managing large amounts of data.

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Introduction to Database Management Systems

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  1. CS3431 –Database Systems I Introduction Instructor: Mohamed Eltabakh meltabakh@cs.wpi.edu

  2. Today’s Lecture • Overview on Database Management Systems • Course Logistics

  3. What is a Database System? • Software platform for managing large amounts of data • Managing means: • Storing, querying, indexing, and structuring the data • Different names refer to the same thing: • Database systems • Database management systems • DBMS

  4. What is a Database System? (Cont’d) • What’s inside a DBMS • Collection of interrelated data (E.g., for a given application) • Set of programs to secure and access the data • An environment that is both convenientand efficientto use • Usually data is too large to fit in computer memory at once • Data stored on disk • Usually many users want to access this data and do so fast • Databases touch all aspects of our lives. We use it without knowing !!!

  5. ? Database Applications Have you ever used a database application? • E-commerce: books, equipment etc. at Amazon • Banks -- your valuable $$ and ATM transactions • Airlines – manage flights to get you places • Universities – manage student enrollment • GIS (Maps) – find restaurants closest to WPI • Bio-informatics (genome data) Data is everywhere. To efficiently manage it, we need DBMS

  6. Why use DBMS, and not files? Several drawbacks of using file systems • Data redundancy and inconsistency • Multiple file formats, duplication of information in different files • Multiple records formats within the same file • No order enforced between fields • Difficulty in accessing data • Need to write a new program to carry out each new task • No indexes, always scan the entire file • Integrity problems • Modify one file (or field in a file), and not changing the dependent fields or files • Integrity constraints (e.g., account balance > 0) become “buried” in program code rather than being stated explicitly

  7. Why use DBMS, and not files? (Cont’d) • Concurrent access by multiple users • Many users need to access/update the data at the same time (concurrent access) • Uncontrolled concurrent access can lead to inconsistencies • Example: Two people are updating the same bank account at the same time • Security problems • Hard to provide user access to some, but not all, data • Recovery from crashes • While updating the data the system crashes • Maintenance problems • Hard to search for or update a field • Hard to add new fields

  8. DBMS Provides Solutions • Data consistency even with multiple users • Efficient access to the data • Data integrity embedded in the DBMS • Recovery from crashes, security

  9. Basic Terminology • Data Model • Tools used for describing the data • Data Schema • Describes structures for a particular application, using the given model • Database • Collection of actual data that conforms to given schema • Database Management System (DBMS) • Software platform that allows us to create, stores, use, and maintain a database • Data Manipulation Language (DML) • Language to manipulate, e.g., update or query, the data

  10. Data Model • A collection of tools for describing • Data • Data relationships • Data semantics • Data constraints • Several data models: • Relational model • Entity-Relationship (ER) data model • Object-based data models (Object-oriented) • Semi-structured data model (XML) • Other older models: • Network model • Hierarchical model We will learn these two models

  11. Example: ER Model • Graphical model for describing entities, attributes, and relationships

  12. Data Schema • Captures the relationships between objects (“entities”) in an application • Schemas can be represented graphically or textual

  13. Query Language (SQL) • Language for accessing and manipulating the data organized by the appropriate data model • SQL: Structured Query Language SELECTID, Name FROM Student WHEREaddress=“320FL”;

  14. Query Language • Two classes of languages • Procedural– user specifies what data is required and how to get those data • Declarative (non-procedural) – user specifies what data is required without specifying how to get those data • DBMSs use declarative language (SQL) SELECTID, Name FROM Student WHEREaddress=“320FL”;

  15. A Big Picture of What You will Learn

  16. You will Learn • Data Model • Relational Model • Entity-Relationship (ER) Model • Data Schema • How to put pieces together to build a schema describing the application • Database • Build an actual database and manipulate data • Database Management System (DBMS) • We will use Oracle • Query Language • SQL Language

  17. Relational Data Model: Overview • The most widely used model today • It is a tabular representation of the data • Main concepts: • Relations (Tables),basically a table with rows and columns. • Every relation has a schema, which describes the columns, or fields. Field or attribute

  18. Example Database : Relational Tabular View of Data in Airline System Flight Passenger Travel • Tabular view of data is called “Relational Model”

  19. Entity-Relationship Model: Overview • Models the application as a collection of entities and relationships • Represented using Entity-Relationship Diagram (ERD)

  20. SQL: Overview • SQL: Non-procedural language to access the data inside a database • External programs, e.g., in C or Java, typically access the database using: • Language extensions to allow embedded SQL • ODBC: Open Database Connectivity • JDBC: Java Database Connectivity

  21. Logical vs. Physical How this information is stored???

  22. Levels of Abstraction • View Level --describes how users see the data • Logical Level – describes the logical structures used • Relational Model • ERD model • Physical Level -- describes files and indexes Usually hidden from users

  23. Levels of Abstraction: Airline Application Example • Logical (Conceptual) Level • Flight, Passenger, Travel tables • Physical Level • Flight table stored as a sorted file on the flight number • Index on flightNo attribute for Flight relation • View Level (External Schema) • NoOfPassengers (flightNo, date, numPassengers) • Hide employees salary These levels of abstraction lead to “Data Independence”

  24. Data Independence • DBMS has the three levels of abstractions • Ability to modify one level without affecting the other levels • Physical data independence: • Physical schema such as indexes can change, but logical schema need not change • Protection from changes in physical structure of data • Logical data independence: • Logical schema can change, but views need not change • Protection from changes in logical structure of data

  25. Other Advanced Aspects of DBMSs • Efficient access • Query optimization • Concurrency control • Recovery control >> We will not have time to study these subjects during the course >> It is important to know their existence and what is meant by each component

  26. Efficient Access • Indexing • Indexes gives direct access to “necessary” portion of data, as opposed to sequential access in files Directly find this customer without scanning all customers

  27. Query Optimization • Costing: • Estimate expected execution times • Query optimization : • Generates many alternatives to answer a query • Estimates the cost of each alternative • Automatically determine and prepare optimal (or near optimal) access plans for getting the data SELECTID, Name FROM Student WHEREaddress=“320FL”; Optimizer = “The Bread and Butter of a DBMS !”

  28. Concurrency Control • DBMS ensures data is consistent under concurrent access • E.g.: multiple airline staff trying to reserve a seat for different customers • Concepts: • Transactions – grouping multiple instructions (reads/writes) into one atomic unit • Locks – locking of resources (tables)

  29. Recovery Control • If system crashes in middle of transaction, recovery must be provided : • Cannot afford to loose data or leave it inconsistent • Concepts: • Logging of transactions’ actions • Ability to redo or undo transactions

  30. Who uses databases? • End users • DB application programmers • Database Administrators • Database design • Security, Authorization • Data availability, crash recovery • Database tuning (for performance)

  31. Summary : Why study DBMS? • Need to process large amounts of data efficiently • Video, WWW, computer games, geographic information systems (GIS), genome data, digital libraries, etc. • Make use of all functionalities provided by DBMSs • DB administrators and programmers hold rewarding jobs • DB research is one of the most exciting areas in Computer Science !!

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