1. 1 IS698: Database Management Min Song IS NJIT

2. 2 Overview  Data Models, Schemas & Instances  Three-Schema Architecture and Data Independence  Database Languages & Interfaces  Database System Environment  Centralized DB & Client/Server Architecture  DBMS Classifications

3. 3 Data Models

4. 4 What is a Data Model?  An abstract representation  Hides low level details  Describes DB structure  Data types  Relationships  Constraints  + (current trend)  Dynamic aspects: E.g. user-defined operations

5. 5 Data Model: Categories (1/3)  High level : from the user perspective  For end user/customer  Entity, attribute, relationships  E-R diagrams

6. 6 Data Model: Categories (2/3)  Low level : how data stored in computer  For computer specialists/DBMS implementer  Physical data model  Record formats, record orderings, access paths

7. 7 Data Model: Categories (3/3)  Representational (implementation) model  Meant for end user  With some of the data organizational information  Can be implemented directly in a computer  E.g. Relational data model  Out of fashion  Network data model  Hierarchical data model

8. 8 Database Schemas

9. 9 What is DB Schema?  A description of the database (meta-data)  Covers only some aspects  E.g. name of record type, data items, some constraints  Not changed frequently  Specify when a new database defined  Meta-data = DBMS Catalog  Schema constructs: Objects in schema  Schema diagram  Convention to display schema

10. 10 Example: University Database DB Schema A DB Instance Schema Constructs

11. 11 Database Instances  Data in the database at a particular time  Instance  = snapshot  = database state  ~= current set of occurrences  DB_state(i)  insert/delete/update  DB_state(i+1)

12. 12 Schema, Instances & DB States  Define DB schema  DB_state(0) = empty state  DB_state(0)  populate  initial state  DB_state(i) is a valid state for all I  Satisfies the structure and the constraints defined in the schema  DB Schema = intention of the database  DB state = extension of the Schema

13. 13 Three-Schema Architecture

14. 14 What is Three-Schema Architecture?  Important characteristics of a database  Insulation of programs and data  Support for multiple user views  Use of catalogs for schemas  Three-Schema architecture implements above characteristics

15. 15 Visualization of Three-Schema Architecture

16. 16 What is in each Schema?  Internal Schema  Physical storage structure  data storage details, access path  Conceptual Schema  Structure of the entire database  Entities, data types, relationships, user operations, constraints  External Schema  Part of the database interested to a particular user group

17. 17 Mapping between Database Schemas  Process of transforming requests among different database level (schemas)  Is a overhead in compilation & execution of queries  Time consuming  Only some of the DBMSs implements Three-schema architecture

18. 18 Data Independence

19. 19 What is Data Independence?  Ability to change one level schema without affecting other levels of schema  Three-schema architecture implements concept of data independence  Only the mapping need to be changed  Logical Independence  Capacity to change conceptual schema without affecting external view (application programs)  Physical Independence  Ability to change internal schema without changing the conceptual view

20. 20 Logical Data Independence CONCEPTUAL VIEW 1 EXTERNAL VIEW

21. 21 Database Languages

22. 22 Purpose of a Database Language  DDL (Data Definition Languages)  Conceptual schema  Internal schemas (when schema separation is not clear)  External schema (in most DBMSs)  SDL (Store Definition Languages)  Internal schema  VDL (View Definition Languages)  External view  DML (Data Manipulation Languages)  To manipulate the populated data  Modern DB  All in one (E.g. SQL)  Separate SDL

23. 23 Data Manipulation Languages  High-level (nonprocedural)  Set-at-a-time/set oriented  Declarative  Complex DB operations  Interactive/embedded in programming languages  Low-level (procedural)  Record-at-a-time  Embedded in general purpose programming languages

24. 24 Where the DML is Used?  When DML is embedded in program  Programming Language  host language  DML  data sub language  For interactive queries  DML  query language  General users  User friendly interfaces

25. 25 DBMS Interfaces  Menu-Based Web Interfaces  Forms-Based Interfaces  Graphical User Interfaces  Natural Language Interfaces  Interfaces for parametric Users  Interfaces for DBA

26. 26 The Database System Environment

27. 27 Components of DBMS:

28. 28 Relational System Architecture  Databases are BIG pieces of software. Typically very hard to modularize. Lots of system design decisions at the macro and micro scale. Here we focus on macro design.  Disk management choices:  file per relation  big file in file system  raw device  Process Model:  process per user  server  multi-server

29. 29 Relational System Architecture: Continue  Basic modules:  parser  query rewrite  optimizer  query executor  access methods  buffer manager  lock manager  log/recovery manager

30. 30 Relational System Architecture: Continue  Query Rewriter  Flattens views  may change query semantics (constraints, protection, etc.)  Optimizer  large space of equivalent relational plans  pick one that’s going to be "optimal"  produces either an interpretable plan tree, or compiled code  Executor  modules to perform relation operations like joins, sorts, aggregations, etc.  calls Access Methods for operations on base and temporary relations  Access Methods  uniform relational interface (open, get next), a la INGRES AMI, System R's RSS  multiple implementations: heap, B-tree, extensible hashing

31. 31 Relational System Architecture: Continue  Buffer Manager  Intelligent user-level disk cache  must interact with transaction manager & lock manager  Lock Manager  must efficiently support lock table  System R architecture influential:  physical and logical locks treated uniformly  multiple granularity of locks  set intent locks at high levels  we will study this in more detail later (Gray)  deadlock handling: detection

32. 32 Relational System Architecture: Continue  Log/Recovery Manager  "before/after" log on values  checkpoint/restore facility for quick recovery  Redo/Undo on restore  Support soft crashes off disk, hard crashes off tape.  System R’s shadowing is too slow. Use Write-Ahead Logging! (WAL) Hard to get right!

33. 33 Software Components of a DBMS  DBMS Component Modules  Database System Utilities  Tools  Application Environments  Communication Facilities

34. 34 DBMS Component Modules (1/2)

35. 35 DBMS Component Modules (2/2)  Disk access control  Stored Data Manager  OS  Buffer Manager Module  Compilers  DDL Compiler  Query Compiler  DML Compiler  Precompiler/Host language compiler  Handling DB access at runtime  Runtime database processor

36. 36 Database System Utilities  Loading: load/transfer using files  Conversion tools  Backup: copy/dump databases  Failure recovery  Incremental backups  File reorganization: to improve performance  Performance/access Monitoring  Sorting/data compression/interfacing to network

37. 37 Tools  CASE: Computer Aided Software Engineering Tools  DB designers/DBA/users  Design phase  Information repository  Data dictionary (data repository) systems  Catalog/design decisions/usage standards/application program descriptions/user information

38. 38 Application Development Environments  E.g. PowerBuilder/JBuilder  Supports  Development of database applications  Database design  GUI development  Querying and updating

39. 39 Communication Software  Provide access for remote users  DB/DC package  Supports for distributed DBMSs

40. 40 DBMS Architectures

41. 41 Centralized DBMSs

42. 42 Basic Client/Server Architecture  Applied for network with  PCs, workstations, printers, file servers, database servers, web servers, etc  Specialized server with specific functionalities  Many clients access specialized server  Client machine provide interfaces  Utilizes processing power of the clients

43. 43 Client/Server Architecture for DBMSs

44. 44 Two-Tier Architecture  Relational DataBase Management Systems (RDBMS)  Query Server/Transaction Server/SQL Server  Open DataBase Connectivity (ODBC)  Application Program Interface (API)  Client/server approach in OO-DBMS: Data Server

45. 45 Three-Tier Architecture  User interface  Application rules  Middle tier  Application server/Web server  Data access

46. 46 DBMS Classifications

47. 47 DBMS Classification Based on Data Model  Relational data model  Object data model  Object-relational data model  Extended-relational model  XML Model  Hierarchical data model  Network data model

48. 48 DBMS Classification Based on Number of Users  Single-user systems  Multi-user systems

49. 49 DBMS Classification Based on Number of Sites  Centralized systems  Distributed DBMSs (DDBMS)  Homogeneous DDBMS  Heterogeneous DBMS (Federated DBMS/multi-database systems)

50. 50 DBMS Classification – More Criteria  Cost  Type of access path  Purpose  General purpose  Special purpose  E.g. Airline system (OLTP – Online transaction processing systems)

51. 51 Summary  Data Models  Database Schemas  DB Languages  DBMS Interfaces  DB System Environment  DBMS Architectures  DBMS Classifications

52. 52 Questions? Thank you!