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Part seven: Modern IT Architecture Desktop Systems (one computer) PC Hardware Software Systems Distributed Systems (many computer) Computer Networks and the Internet Distributed application and Client/Server The World Wide Web and e-commerce Databases Technology 1. Database Concepts 2. Microsoft Access 3. Database Trends FILE ORGANIZATION A computer system organizes data in a hierarchy that begins with bits, and proceeds to bytes, fields, records, files, and database. File Record Field Byte Record Field Byte Byte Bit Field Bit Filed Byte Bit Bit FILE ORGANIZATION BIT: Binary Digit (0,1;Y,N;On, Off) BYTE: Combination of BITS which represent a CHARACTER FIELD: A logical grouping of characters into a word, a group of words, or a complete number. RECORD: Collection of FIELDS which reflect a TRANSACTION FILE: A Collection of Similar RECORDS DATABASE: An Organization’s Electronic Library of FILES FILE ORGANIZATION A record For Example, Filed: Student’s name; Record: Number Name Course Date Grade 9525012 Zhang Yan MIS 1998.9 A Name Course Date Grade Zhang Yan 9525018 Jeff Yu MIS 1998.9 A MIS 1998.9 A 9525027 … He Hui MIS 1998.9 B … … … … •File: Number 9525012 FILE ORGANIZATION : Another way of thinking about database components—— ENTITY: Person, Place, Thing, Event about Which Data Must be Kept ( a record describes an entity ) ATTRIBUTE: Description of a Particular ENTITY (corresponds to fields) KEY FIELD: Field Used to Retrieve, Update, Sort RECORD * FILE ORGANIZATION Record Key Field Attribute Key Field FDU NO. HKU NO. NAME SEX 98HM001 93835 Xie Mingqiang M 58702331 98HM002 93840 Yu Bing F 65110968 98hm003 93841 Wang Pei F 58711001 -23306 63568504 98HM004 93842 Ge Ruijin M 56938860 56873143 98HM005 93843 Wang Xintao M 58611828 65352394 98HM006 93844 Fu Qiang F 58666060 -6007 58836304 File TEL(O) TEL(H) KEY FIELD Field in Each Record Uniquely Identifies THIS Record For RETRIEVAL UPDATING SORTING * Accessing Records from Computer Files:Sequential vs. Direct or random fileData organization SEQUENTIAL: records must be retrieved in the same physical sequence in which they are stored. (Magnetic tape ) DIRECT: Data can be accessed without regard to physical sequence. (Disk) * Direct file organization Sequential file organization Problems Arising from the File Organization Data Redundancy: The same piece of information could be duplicated in several files. Data Inconsistency: Data Isolation: Data files are likely to be organized differently, stored in different formats, and often physically inaccessible to other applications. data integrity problem: It is difficult to place data integrity constraints across multiple data files. Application and Data Independence: In the file environment, the applications and their associated data files are dependent on each other. Poor security: is difficult to enforce in the file environment. Lack of data sharing & availability Problems Arising from the File Organization Data Redundancy; Data Inconsistency; Data Isolation, data integrity problem; Application and Data Independence; Security, data sharing problem. These problems led to the development of DATABASE DATABASE A Database is an organized logical grouping of related files. In a Database, data are stored & managed in a convenient form, and integrated and related so that one set of software programs provides access to all the data. DATABASE MANAGEMENT SYSTEM (DBMS) Software to create & maintain DATA enables business applications to extract data independent of specific computer programs. registrar Class programs Class file accounting Accounts programs Class file athletics Sports programs Class file Computer based files of this type cause problems such as redundancy, inconsistency, and data isolation. registrar accounting Class programs Accounts programs DBMS Database Class file Accounts file Sports file athletics Sports programs DBMS provides access to all data in the database COMPONENTS OF DBMS: DATA DEFINITION LANGUAGE: DATA MANIPULATION LANGUAGE: Defines Data Elements in Database Manipulates Data for Applications DATA DICTIONARY: Formal Definitions of all Variables in Database; Controls Variety of Database Contents * TWO VIEWS OF DATA PHYSICAL VIEW: WHERE IS DATA PHYSICALLY? DRIVE, DISK, SURFACE, TRACK, SECTOR (BLOCK), RECORD TAPE, BLOCK, RECORD NUMBER (KEY) LOGICAL VIEW: WHAT DATA IS NEEDED BY APPLICATION? SUCCESSION OF FACTS NEEDED BY APPLICATION NAME, TYPE, LENGTH OF FIELD * Database Structures HIERARCHICAL DATABASE ROOT FIRST CHILD 2nd CHILD Employer Compensation Ratings Salary Job Assignments Pension Benefits Insurance Health Type of RELATIONS ONE-TO-ONE: STUDENT CLASS ONE-TO-MANY: STUDENT A MANY-TO-MANY: ID STUDENT B CLASS 1 STUDENT A STUDENT C CLASS 2 STUDENT B STUDENT C NETWORK DATA MODEL Variation of Hierarchical Model Useful for many-to-many relationships CLASS 1 STUDENT A CLASS 2 STUDENT B STUDENT C RELATIONAL DATA MODEL DATA IN TABLE FORMAT RELATION: TABLE Tuple: ROW (RECORD) IN TABLE Field: COLUMN (ATTRIBUTE) IN TABLE * HOURS RATE TOTAL ABLE $ 40.50 $ 10.35 $ 419.18 BAXTER $ 38.00 $ 8.75 $ 332.50 CHEN $ 42.70 $ 9.25 $ 394.98 DENVER $ 35.90 $ 9.50 $ 341.05 The Relational Database Model The relational model is based on a simple concept of tables in order to capitalize on characteristics of rows and columns of data, which is consistent with real-world business situations. Tables are called relations, and the model is based on the mathematical theory of sets and relations. A row is called a tuple, and a column is called an attribute. One of the greatest advantages of the relational model is its conceptual simplicity and the ability to link records in a way that is not predefined. Example DB: Fortune 500 Companies company compname sales assets netincome empls indcode yr allied 9115000 13271000 -279000 143800 37 85 boeing 9035000 7593000 292000 95700 37 82 ... industry codes indcode indname 42 pharmaceuticals 44 computers ... The Relational Abstraction Information is in tables Columns define attributes Also called fields or domains Rows define records Also called (base) relations Also called tuples Cells contain values All cells in column have information of same type e.g., integer, floating point, text, date Operations on Tables Add new rows (or sometimes columns) Modify existing rows Choose a subset of columns Choose a subset of rows Combine rows (e.g., sum values in a column) Combine columns Combine two tables (join) No operations to combine individual cells Unlike spreadsheet Operating on Databases: SQL Every abstraction needs an interface through which users invoke abstract operations graphical interface language Structured Query Language Has all those operations We'll focus only on queries Query = question Extract some data from one or more tables to answer a particular question Physical vs. Logical Data View How can a single, unified database meet the differing requirements of so many users? Minimizes these problems by providing two “views” of the database data: The physical view deals with the actual, physical arrangement and location of data in the direct access storage devices (DASD). The logical view, or user’s view, represents data in a format that is meaningful to a user and to the software programs that process that data. 2. Microsoft Access Features: Create/Modify databases Specify/Run queries Design/Print reports Design graphical user interfaces around databases Forms for entering, viewing data An Introduction Microsoft Access GUI Building A GUI is A Set of Forms Forms Used for Entering data to tables Displaying data from tables or queries in a nicer way Each form is usually “bound” to a table or query every “screenful” in the form displays the contents of one record in that table or query Forms contain Controls Text boxes Labels Pictures Buttons Controls Forms contain controls Text labels Text boxes List boxes Combo boxes Option groups Buttons “Objects” created by other applications Pictures Word documents Spreadsheets Decorative lines and boxes Every Control has a set of Properties Properties determine where the control gets its data from how it is displayed Usually properties are automatically set by wizards users only need to occasionally fine-tune them Creating Forms Easy way: use an Access Wizard Difficult way: manually add controls Editing a form’s design Select “Design View” Modify controls Modify properties move them, resize them, delete them right-click on a control to get to its property list Add new controls make Toolbox visible by selecting it from the “View” menu drag and drop new controls from the Toolbox set the properties of the new controls Reports Specify the structure of printed reports Similar structure to forms Every report is bound to a table or query Reports have controls, where every control specifies how a specific field of a record in the table/query will appear Access provides wizards for easy creation of new reports Users typically only need to fine-tune them Report Examples Category Sales for 1995 New report, select Report Wizard Base on query “Category Sales for 1995” Select both fields, no grouping, sort by “Category Name” Tabular Layout, Corporate Style Store as “Category Sales for 1995” Switch to “Design View”, add a text box in Report Footer to show “Total Sales” Access GUI Summary 2. A form displays records from a table or query 1. A GUI is a set of forms 3. A form has a set of controls 4. A control displays data from a field or accepts user input 5. A control has a set of properties 6. User interaction with forms/controls generates events 7. Macros can be attached to form/control event properties Macros Allow programmers to build functionality into MS Access forms Connect to forms and controls through events Typical Uses of Macros Open Forms from inside other Forms Synchronize data in two open Forms when data changes in one form, corresponding data also changes on the other form Find a record which satisfies given properties more user-friendly that writing queries Validating input data Events “Certain things that happen on the form or control” Mouse clicks/double clicks Form open/close Control value changed etc. Controls have one property per event type Determines what happens when event is triggered Can be connected to a macro Most Important Event Properties On Click On DoubleClick After Update triggered when we click/doubleclick on a control triggered after we have changed the value of a control On Current Triggered every time a new record is displayed in a Form Macro Structure Each macro is a set of sequential actions Each action has a set of parameters Actions may (optionally) be conditional Macros can be named and saved (just as tables,queries, forms) Macro Example Conditions Parameters for current action Actions Comments Explanation of parameters 3. Database Trends(1) The evolution of Database System Data Simple data => Multimedia data, Knowledge Model Relational model => OO model Object relational model Databases Trends (2) Application Data organization OLTP => OLAP Database => Data warehouse, Data Marts Query language SQL => Deductive Emerging Database Models The most common database models are: Multimedia database Deductive databases Object-oriented databases Multimedia and hypermedia databases Object-Oriented Database Model Object-oriented (OO) databases store both data and procedures acting on the data, as objects. The OO database can be particularly helpful in multimedia environments, such as in manufacturing sites using CAD/CAM. OO databases can be particularly useful in supporting temporal and spatial(时空) dimensions. Terminology in the OO model includes: objects, attributes, classes, methods, and messages. Hypermedia Database Model The hypermedia database model stores chunks of information in the form of nodes connected by links established by the user. The nodes can contain text, graphics, sound, full-motion video, or executable computer programs. Users can branch to related information in any kind of relationship. Thanks for Your Attention