Database system concepts and architecture Jan. 2008Yangjun Chen ACS Outline: Concepts and Architecture Database schema Working process with a database system Database system architecture Data independence concept Database language Database application Interfaces Database environment

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Schema: a description of a database -- meta data the intension of the database Schema evolution: if the database definition changes, we say it evolves. Database State: the data in the database at a particular point in time the extension of the schema

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Sample database Student Name StNo Class Major Smith 17 1 CS Brown 8 2 CS Course CName CNo CrHrs Dept Database CS C CS Section SId CNo Semester Yr Instructor Spring 2000 Smith Winter 2000 Smith Spring 2000 Jones Grades StNo SId Grade A B

Database system concepts and architecture Jan. 2008Yangjun Chen ACS University database schema: Course Cnamestring(20) CNo string(20) CrHrsinteger Dept.String(20) grades StNointeger SIdinteger GradeString(20) Student Namestring(20) StNointeger Classinteger MajorString(20) Section SIDinteger CNostring(20) Semesterinteger Yrinteger Instructorstring(20)

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Schema evolution: Course Cnamestring(20) CNostring(20) CrHrsinteger Dept.String(20) Student Namestring(20) StNointeger Classinteger MajorString(20) Prerequisite CNostring(20) Pre-CNostring(20) …... new table added

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Database evolution: Course Cnamestring(20) Cnostring(20) CrHrsinteger Dept.String(20) Student Namestring(20) StNointeger Classinteger MajorString(20) Ageinteger Sexstring(20) …... new attributes added

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Sample database Student Name StNo Class Major Smith 17 1 CS Brown 8 2 CS Course CName CNo CrHrs Dept Database CS C CS Section SId CNo Semester Yr Instructor Spring 2000 Smith Winter 2000 Smith Spring 2000 Jones Grades StNo Sid Grade A B

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Database state changed: Student Name StNo Class Major Smith 17 1 CS Brown 8 2 CS Course CName CNo CrHrs Dept Database CS C CS Section SId CNo Semester Yr Instructor Spring 2000 Smith Winter 2000 Smith Grades StNo Sid Grade A B

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Definition Manipulation Construction We define the database database state is the empty state with no data initial state when database is populated (loaded) current state changes with each insert, delete, update hopefully, the database goes from one correct/valid state to another

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Three-schema architecture External view External view Conceptual schema Internal schema Physical storage structures and details Describes the whole database for all users A specific user or groups view of the database

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Data independence Ability to change the database at one level with no impact to the next higher level physical data independence - the ability to change the physical schema without affecting the conceptual schema typical example: add a new index logical data independence - the ability to change the conceptual schema without affecting existing external views or application programs typical example: add an attribute

Database system concepts and architecture Jan. 2008Yangjun Chen ACS DBMS Languages Data definition language (DDL): used to define the data schema. Ideally one schema definition language per level in practice there might be one for all levels SQL provides DDL capabilities for the conceptual and external levels

Database system concepts and architecture Jan. 2008Yangjun Chen ACS DBMS Languages Data Manipulation language (DML): Used to manipulate data. typical systems provide a general purpose language for inserting, updating, deleting, and retrieving data two distinctions: set-oriented and row-at-a-time

Database system concepts and architecture Jan. 2008Yangjun Chen ACS EXEC SQL DECLARE C1 CURSOR FOR SELECT au_fname, au_lname FROM authors FOR BROWSE; EXEC SQL OPEN C1; while (SQLCODE == 0) { EXEC SQL FETCH C1 INTO :fname, :lname; printf(“the author name is:”, fname, laname); } Database applications If an application program that accesses the database embeds DML commands within it, then we have a host language and a data sublanguage.

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Record-at-a-time procedural - need loops, etc navigate through data obtaining 1 record at a time note that SQL does permit this via cursors Set-oriented operations select Name, StNo from student where Name like “M%” EXEC SQL DELETE FROM authors WHERE au_lname = 'White'

Database system concepts and architecture Jan. 2008Yangjun Chen ACS DBMS interfaces menu-based forms-based GUI – Graphic User Interface natural language for parametric users for dba

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Example of a menu-based interface: from MS Access

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Example of a GUI from StarTracker

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Example of a natural language interface: (from MS SS7) English Query translates a natural-language question about data in the database to a set of SQL SELECT statements that can then be executed against the SQL Server database to get the answer. For example, given a car sales database, an application can send English Query a string containing the question, “How many blue Fords were sold in 2003?” English Query returns to the application an SQL statement such as: SELECT COUNT(*)FROM CarSales WHERE Make = 'Ford’AND Color = 'Blue' AND DATEPART(yyyy, SalesDate) = ’2003' The application can then execute the SQL statement against the SQL Server database to get a number. It can return to the user. Note the comment: English Query works best with a normalized database.

Database system concepts and architecture Jan. 2008Yangjun Chen ACS DBMS environment see figure 2.3 stored data manager A module to control access to DBMS information that is stored on disk, whether it is part of the database or the catalog. DDL compiler A module to process schema definition, specified in the DDL, and store description of the schema (meta-data) in the DBMS catalog. DML compiler It translates the DML commands into object code for database access. run-time database processor It handles database access at run time; it receives retrieval or update operations and carries them out on the database.

Database system concepts and architecture Jan. 2008Yangjun Chen ACS DBMS environment query compiler It handles high-level queries that are entered interactively. It parses, analyzes, and compiles or interprets a query by creating database access code, and then generates calls to the rum-time processor for executing the code. pre-compiler It extracts DML commands from an application program which is written in host programming language like C, Pascal, etc.

Database system concepts and architecture Jan. 2008Yangjun Chen ACS DBMS utilities loading loading existing files - such as text files or sequential files - into the database. Backup creating a backup copy of the database, usually by dumping the entire database into tape. file reorganization reorganizing a database file into a different file organization to get a better performance. performance monitoring monitoring database usage and providing statistics to the DBA.

Database system concepts and architecture Jan. 2008Yangjun Chen ACS Classifying DBMSs data model: relational / object-orieted / hierarchical / network / object- relational users: single-user / multi-user location: distributed / centralized cooperation: homogeneous / heterogeneous OLTP: on-line transaction processing Used to run the day-to-day operations of a business event-oriented: take an order, make a reservation, payment for goods, withdraw cash,...