Database models unit 1 part 2
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The document outlines the evolution of database models from the 1960s to the present, highlighting the transition from file-based systems to relational databases. It discusses the principles of relational databases, including their advantages such as structural independence and ad-hoc querying through SQL, as well as their disadvantages like system complexity and potential for poor design. The document also introduces the Entity-Relationship (E-R) model, emphasizing its role in visualizing data relationships and aiding in database design.
Database models unit 1 part 2
- 2. Evolution of Database ModelsTimeline 2 1960s 1970s 1980s 1990s 2000+ File-based Hierarchical Network Relational Object-oriented Web-based Entity-Relationship
- 3. Database: Historical Roots Manual File System ◦ to keep track of data ◦ used tagged file folders in a filing cabinet ◦ organized according to expected use ◦ e.g. file per customer ◦ easy to create, but hard to ◦ locate data ◦ aggregate/summarize data Computerized File System ◦ to accommodate the data growth and information need ◦ manual file system structures were duplicated in the computer ◦ Data Processing (DP) specialists wrote customized programs to ◦ write, delete, update data (i.e. management) ◦ extract and present data in various formats (i.e. report) 3
- 4. File System: Example 4 Database Systems: file based database of different Sections
- 5. File System: Weakness Weakness ◦ “Islands of data” in scattered file systems. Problems ◦ Duplication ◦ same data may be stored in multiple files ◦ Inconsistency ◦ same data may be stored by different names in different format ◦ Rigidity ◦ requires customized programming to implement any changes ◦ cannot do ad-hoc queries Implications ◦ Waste of space ◦ Data inaccuracies ◦ High overhead of data manipulation and maintenance 5
- 6. File System: Problem Case 6 CUSTOMER file AGENT file SALES file A_Name (15 char) Carol Johnson A_Name (20 char) Carol T. Johnson AGENT (20 char) Carol J. Smith - inconsistent field name, field size - inconsistent data values - data duplication
- 7. Database System vs. File System 7 Database Systems: Comparison between file system and DBMS
- 8. Relational Database Problems with legacy database systems ◦ Required excessive effort to maintain ◦ Data manipulation (programs) too dependent on physical file structure ◦ Hard to manipulate by end-users ◦ No capacity for ad-hoc query (must rely on DB programmers). Evolution in Data Organization ◦ E. F. Codd’s Relational Model proposal ◦ Separated the notion of physical representation (machine-view) from logical representation (human-view) ◦ Considered ingenious but computationally impractical in 1970 ◦ Relational Database Model ◦ Dominant database model of today ◦ Eliminated pointers and used tables to represent data ◦ Tables ◦ flexible logical structure for data representation ◦ a series of row/column intersections ◦ related by sharing common entity characteristic(s) 8
- 9. Relational Database: Example 9 Provides a logical “human-level” view of the data and associations among groups of data (i.e., tables) Customer_ID Customer_Account Agent_ID 1224 4556 23 1225 4558 25 Agent_ID Last_Name First_Name Phone 23 Sturm David 334-5678 25 Long Kyle 556-3421 Customer_ID Last_Name First_Name Phone Account_Balance 1224 Vira Dyne 678-9987 1223.95 1225 Davies Tricia 556-3342 234.25
- 10. Relational Database: Pros & Cons Advantages ◦ Structural independence ◦ Separation of database design and physical data storage/access ◦ Easier database design, implementation, management, and use ◦ Ad hoc query capability with Structured Query Language (SQL) ◦ SQL translates user queries to codes Disadvantages ◦ Substantial hardware and system software overhead ◦ more complex system ◦ Poor design and implementation is made easy ◦ ease-of-use allows careless use of RDBMS 10
- 11. Entity Relationship Model Peter Chen’s Landmark Paper in 1976 ◦ “The Relationship Model: Toward a Unified View of Data” ◦ Graphical representation of entities and their relationships Entity Relationship (ER) Model ◦ Based on Entity, Attributes & Relationships ◦ Entity is a thing about which data are to be collected and stored ◦ e.g. EMPLOYEE ◦ Attributes are characteristics of the entity ◦ e.g. SSN, last name, first name ◦ Relationships describe an associations between entities ◦ i.e. 1:M, M:N, 1:1 ◦ Complements the relational data model concepts ◦ Helps to visualize structure and content of data groups ◦ entity is mapped to a relational table ◦ Tool for conceptual data modeling (higher level representation) ◦ Represented in an Entity Relationship Diagram (ERD) ◦ Formalizes a way to describe relationships between groups of data 11
- 12. E-R Diagram: Relationships Entity ◦ represented by a rectangle with its name in capital letters. Relationships ◦ represented by an active or passive verb inside the diamond that connects the related entities. Connectivities ◦ i.e., types of relationship ◦ written next to each entity box. 12 Database Systems: Design, Implementation, & Management: Relationships
- 13. E-R Model: Pros & Cons Advantages ◦ Exceptional conceptual simplicity ◦ easily viewed and understood representation of database ◦ facilitates database design and management ◦ Integration with the relational database model ◦ enables better database design via conceptual modeling Disadvantages ◦ Incomplete model on its own ◦ Limited representational power ◦ cannot model data constraints not tied to entity relationships ◦ e.g. attribute constraints ◦ cannot represent relationships between attributes within entities ◦ No data manipulation language (e.g. SQL) ◦ Loss of information content ◦ Hard to include attributes in ERD 13
- 14. Web Database : Future of DBMS Internet is emerging as a prime business tool ◦ Shift away from models (e.g. relational vs. O-O) ◦ Emphasis on interfacing with the Internet Characteristics of “Internet age” databases ◦ Flexible, efficient, and secure Internet access ◦ Support for complex data types & relationships ◦ Seamless interfaces with multiple data sources and structures ◦ Ease of use for end-user, database architect, and database administrator ◦ Simplicity of conceptual database model ◦ Many database design, implementation, and application development tools ◦ Powerful DBMS GUI 14