Chapter 3. Database Architecture and the Web

Transcription

1 Chapter 3 Database Architecture and the Web 1

2 Chapter 3 - Objectives Software components of a DBMS. Client server architecture and advantages of this type of architecture for a DBMS. Function and uses of Transaction Processing Monitors. Web-Services and Service-Oriented Architectures Distributed DBMSs 2

3 Components of a DBMS DBMS is partitioned into several software components/modules Assigned with to specific operation Design of a DBMS must take into account the interface between the DBMS and the OS 3

4 Components of a DBMS o o o Query processor o a major DBMS component that transform queries into a series of low-level instructions directed to the db manager. Database Manager (DM) o o accepts queries & examines the external & conceptual schemas to determine what conceptual records are required to satisfy the request DM places a call to the file manager to perform the request. File manager o o o manipulates the underlying storage files & manages the allocation of storage space on disk. It establishes and maintains the list used, calls on the hashing functions to generate record addresses. It passes the requests on to the appropriate access methods(either read or write data from system buffer) 4

5 Components of a DBMS o o o DML preprocessor o o converts DML statements embedded in an application program into standard function calls in the host language DML processor must interact with the query processor to generate the appropriate code DDL compiler o o converts DDL statements into a set of tables containing metadata. These tables are then stored in the system catalog Catalog manager o manages access to and maintains the system catalog 5

6 Components of Database Manager (DM) Authorization control this module checks & confirms whether the user has the necessary authorization to carry out the required operation Command processor once the system confirmed the user has authority to carry out operation, control is passed to the command processor. Integrity checker for an operation that changes the db, the integrity checker checks whether the requested operation satisfies all necessary integrity constraints. Query optimizer determines an optimal strategy for the query execution Transaction manager performs the required processing of operations that it receives from transactions Scheduler responsible for ensuring that concurrent operations on the db proceed without conflicting with one another Recovery manager ensures that the db remains in a consistent state in the presence of failure Buffer manager responsible for the transfer of data between 6 main memory & secondary storage (such as disk and tape)

7 Multi-User DBMS Architectures Common architectures used to implement multi-user database management systems: Teleprocessing File-server Client-server 7

8 Teleprocessing Traditional architecture. Single mainframe with a number of terminals attached. User terminals dumb Incapable of functioning on their own 8

9 File-Server File-server is connected to several workstations across a network. Database resides on file-server. DBMS and applications run on each workstation. Disadvantages include: Significant network traffic. Copy of DBMS on each workstation. Concurrency, recovery and integrity control more complex. 9

10 File-Server Architecture The processing is distributed about the network (LAN) The file-server holds the files required by the applications and the DBMS Applications and the DBMS run on each workstation File-server acts as a shared hard disk drive 10

11 Traditional Two-Tier Client-Server Client (tier 1) manages user interface and runs applications. (responsible for the presentation of data to the user) Server (tier 2) holds database and DBMS. (responsible for supplying data services to the client) Advantages include: wider access to existing databases; increased performance; possible reduction in hardware costs; reduction in communication costs; increased consistency. 11

12 Traditional Two-Tier Client-Server The client takes the user s request, checks the syntax, and generates database requests in SQL Then transmits the message to the server, waits for a response, and formats the response for the end-user. The server accepts and processes the database requests, then transmits the results back to the client. The processing involves checking authorization, ensuring integrity, maintaining the system catalog, query and update processing. 12

13 Traditional Two-Tier Client-Server 13

14 Three-Tier Client-Server In two tier client-server, client side presented two problems preventing true scalability: Fat client, requiring considerable resources on client s computer to run effectively. Significant client-side administration overhead. By 1995, three layers proposed, each potentially running on a different platform. 14

15 Three-Tier Client-Server The three layers: User interface layer Business logic and data processing layer: Application Server DBMS-stores data required by middle tier: Database Server 15

16 Three-Tier Client-Server Advantages: Thin client, requiring less expensive hardware. Application maintenance centralized. Easier to modify or replace one tier without affecting others. Separating business logic from database functions makes it easier to implement load balancing. Maps quite naturally to Web environment. 16

17 Three-Tier Client-Server 17

18 Transaction Processing Monitors Program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for Online Transaction Processing (OLTP). Middleware component that provides access to the services of a number of resource managers (DBMSs, OS, User interfaces, messaging software) Provide a uniform interface for programmers who are developing transactional software (Software that guarantees that all appropriate databases are updated from a single transaction) 18

19 Transaction Processing Monitors Advantages: Transaction routing: increase scalability by directing transactions to specific DBMSs Managing distributed transactions: manage transactions that require access to data held in multiple, possibly heterogeneous DBMSs. Load balancing: balance client request across multiple DBMSs Funneling: handle large users Increased reliability: act as Transaction Manager, performing necessary actions to maintain the consistency of the database 19

20 TPM as middle tier of 3-tier client-server 20

21 Web Services A software system designed to support interoperable machine-to-machine interaction over a network Examples: Microsoft Virtual Earth Web services Amazon S3 Geonames DOTS web services 21

22 Web Services: Microsoft Virtual Earth Web services Offer static map images match addresses to the map, search for points of interest, integrate maps and imagery, return driving directions, and incorporate other location intelligence into your Web application. 22

23 Web Services: Microsoft Virtual Earth Web services 23

24 Web Services: Microsoft Virtual Earth Web services 24

25 Web Services: Microsoft Virtual Earth Web services 25

26 Web Services: Amazon S3 Simple web services interface Can be used to store and retrieve large amounts of data from anywhere on the web Give developer access to the same highly scalable, reliable, fast, inexpensive data storage infrastructure 26

27 Web Services: Amazon S3 27

28 Web Services: Geonames 28

29 Web Services: DOTS web services 29

30 Web Services: DOTS web services 30

31 Web Services Use these technologies and standards: XML SOAP (Simple Object Access Protocol) communication protocol for exchanging structured information over the Internet and uses a messages format based on XML WSDL (Web Services Description Language) protocol based on XML, used to describe and locate a Web service. UDDI (Universal Discovery, Description and Integration) protocol platform-independent, XML-based registry for businesses to list themselves on the Internet.

32 Web Services Web Service XML Interface (WSDL) SOAP 1. Generate 2. Publish Internet Web service directory (UDDI) WSDL documents 3. Find 4. Invoke XML Interface (WSDL) Client Application 32

33 Web Services The growing success of Web services is due to a number of factors, including those below. Systems can interact with one another dynamically via standard Internet technologies. Services are built once and reused many times. Services can be implemented in any programming language. Service consumers do not need to worry about firewalls because communication is carried over HTTP. Systems can advertise their capabilities for other systems to use. 33

34 Distributed Database and DBMS Distributed Database A logically related collection of shared data (and description of this data), physically distributed over a computer network Distributed DBMS The software system that permits the management of the distributed database and makes the distribution transparent to user Distributed Processing A centralized database that can be accessed over a computer network 34

35 Distributed DBMS Site 1 DB DB Computer Network DB Site 2 Site 3 35

36 Characteristics of DDBMS A collection of logically related shared data Data split into a number of fragments Fragments may be replicated Fragments/replicas are allocated to sites Sites are linked by a communication network Data at each site is under control of a DBMS DBMS at each site can handle local applications autonomously Each DBMS participates in at least one global application 36

37 Data Warehousing A consolidated/integrated view of corporate data drawn from disparate operational data sources and a range of end-user access tools capable of supporting simple to highly complex queries to support decision making 37

38 Data Warehousing Architecture Warehouse Manager End-user Access Tools Operational Data Source 1 Operational Data Source 2 Load Manager Metadata Highly Summarized Data Lightly Summarized Data Query Manager Reporting, query, application development and EIS tools Detailed Data OLAP tools Operational Data Source 3 Warehouse Manager Archive/Back up Data Data Mining tools Operational Data Source 4 38