The Client/Server Database Environment
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Transcript The Client/Server Database Environment
Chapter 9:
The Client/Server Database
Environment
註 : 於11版為Chapter 8
楊立偉教授
台灣大學工管系
2013 Fall
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Client/Server Systems
Networked computing model 網路運算模型
Processes distributed between clients and
servers 將要處理的工作散在Client與Server
Client–Workstation (usually a PC) that
requests and uses a service
Server–Computer (PC/mini/mainframe)
that provides a service
For DBMS, server is a database server
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Application Logic in C/S Systems
Presentation Logic 呈現邏輯
Input–keyboard/mouse
Output–monitor/printer
GUI
(Graphic User Interface)
Processing Logic 處理邏輯
I/O processing
Business rules
Data management
Procedures, functions,
programs
Storage Logic 儲存邏輯
Data storage/retrieval
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DBMS activities
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3 types of Client/Server Architectures
Client does
extensive processing
1.File Server Architecture
2.Database Server Architecture
3.Three-tier Architecture
Client does little
processing
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1. File Server Architecture
All processing is done at the PC that requested the
data
FAT CLIENT
Entire files are transferred from the server to the
client for processing Ex. 利用網路芳鄰分享MDB檔
Problems:
Huge amount of data transfer on the network
Each client must contain full DBMS
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Heavy resource demand on clients
Client DBMSs must recognize shared locks, integrity checks, etc.
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Figure 9-2 File server model
FAT CLIENT
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2. Two-Tier Database Server
Architectures
Client is responsible for
I/O processing logic
Some business rules logic
Server performs all data storage and
access processing
DBMS is only on server
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Advantages of Two-Tier Approach
Clients do not have to be as powerful
Greatly reduces data traffic on the network
Improved data integrity since it is all
processed centrally
Stored procedures : performs some
business rules done on server
把較常用或重要的程序預先寫好放在DBMS內
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Advantages of
Stored Procedures
Compiled SQL statements 編譯後執行快
Reduced network traffic 佔較少的網路流量
Improved security 安全性較高
Improved data integrity 資料完整性較高
Thinner clients 前端運算量較少
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Figure 9-3 Database server architecture (two-tier)
Thinner
clients
DBMS only
on server
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3. Three-Tier Architectures
Client
GUI interface
(I/O processing)
Browser
Application server
Business rules
Web Server
Database server
Data storage
DBMS
Thin Client
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PC just for user interface and a little application
processing. Limited or no data storage (sometimes no
hard drive) 例如: Web Browser
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Figure 9-4a Generic three-tier architecture
Thinnest
clients
Business rules
on separate
server
DBMS only on
DB server
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Advantages of Three-Tier
Architectures
Scalability (在佈署與效能上) 具擴充性
Technological flexibility 具技術彈性
Long-term cost reduction 長期低本降低
Better match of systems to business needs
較符合企業所需
Reduced risk 風險降低
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Application Partitioning
Placing portions of the application code in
different locations (client vs. server) AFTER
it is written 重新切分程式執行的位置
Advantages
Improved performance
Improved interoperability
Balanced workloads
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Common Logic Distributions
Figure 9-5a Two-tier clientserver environments
Processing logic could be
at client, server, or both
Figure 9-5b n-tier clientserver environment
Processing logic
will be at
application server
or Web server
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Role of the Mainframe 大型主機
Mission-critical legacy systems tend to remain on mainframes
When moving mission critical systems from mainframe to
distributed client/server systems
例如: 銀行核心系統的移轉
Determining which code belongs on server vs. client
Identifying potential conflicts with code from other applications
Ensuring sufficient resources exist for anticipated load
Rule of thumb 移轉的經驗法則
Mainframe for centralized data that does not need to be moved
Client for data requiring frequent user access, complex graphics, and
user interface
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Benefits of Moving to
Client/Server Architecture
Staged delivery of functionality speeds
deployment 功能可分階段完成
GUI ease application use 將使用者界面與應用分離
Flexibility and scalability facilitates business
process reengineering 更容易擴充 具有彈性
Reduced network traffic 只傳處理過的資料
Facilitation of Web-enabled applications
易於轉為Web或行動應用
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Middleware 中介軟體
Software that allows an application to
interoperate with other software
No need for programmer/user to
understand internal processing
Accomplished via Application Program
Interface (API)
The “glue” that holds client/server applications together
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Database Middleware
ODBC–Open
Database Connectivity
Most DB vendors support this
JDBC–Java
Database Connectivity
可視為Java版的ODBC
Special Java classes that allow Java
applications/applets to connect to databases
OLE-DB
Microsoft enhancement of ODBC
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Using ODBC to Link External Databases
Stored on a Database Server
Open Database Connectivity (ODBC)
Required parameters:
API provides a common language for application
programs to access and process SQL databases
independent of the particular RDBMS that is accessed
ODBC driver
Back-end server name
Database name
User id and password
Additional information:
Data source name (DSN)
Windows client computer name
Client application program’s executable name
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ODBC Architecture
(Figure 9-6)
Client does not need to
know anything about the
DBMS
Application Program
Interface (API) provides
common interface to all
DBMSs
Each DBMS has its own ODBC-compliant driver
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實作: 實際設定一個DSN
(適用Windows作業系統)
控制台→系統管理工具→資料來源(ODBC)
選「系統資料來源名稱」→選「新增」
選一個適當的驅動程式(Driver)
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實際設定一個DSN (續)
填入所需資料並選取Access的MDB檔案,確定即可
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使用ODBC資料來源
以MS Access為例,選檔案→取得外部資料→匯入
選取ODBC來源,選取所需要的DSN即可
適用所有支援ODBC
資料來源的應用程式
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Web/DB Application Components
Database server – hosts the DBMS
Web server – receives and responds to browser
requests using HTTP protocol
e.g. Apache, MS IIS (Internet Information Services)
Application server – software for creating
dynamic web sites
e.g. Oracle, MS SQL Server, MS Access, MySQL
e.g. MS ASP .NET framework, Java EE, PHP
Web browser – client program that sends web
requests and receives web pages
e.g. Internet Explorer, Firefox, Safari, Google Chrome
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Static page requests
.htm or .html requests handled by the Web server
Dynamic page requests
.jsp, .aspx, and .php requests are routed to the
application server
Server-side processing by JSP servlet, ASP .NET
application, or PHP
Database access via JDBC, ODBC, ADO .NET, or
other database middleware
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Figure Information flow in a three-tier architecture
No server side processing, just a page return
Server side processing, including database access
…also *.aspx or *.php
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© 2013 Pearson Education
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