Transcript BICS546 Client/Server Database Application Development

BICS546
Client/Server Database
Application Development
Evolution of Multi-User DBMS Architectures
• Teleprocessing:
– One computer with a single CPU and a number of
dumb terminals.
• File-Server:
– Applications run on workstations that contain a full
copy of the DBMS. File-server acts as a shared hard
disk drive. The DBMS on each workstation sends
requests to the file-server for data.
• Client-Server:
Client-Server
• Client/server is primarily a relationship
between processes running on separate (or
same) machines.
• Client: A process which requires some
resources or services.
• Server: A process which provides the
requested resources or services.
The Three Layers of
Client/Server Systems
• Computer Network
– Network and network operating system provide the platform that
runs the system.
• Client/Server Technology
– Component and distributed object technology, such as COBRA
Common Object Request Broker Architecture, COM Component
Object Model, DCOM, etc., provide the foundation to develop the
system. Database access middleware such as ODBC Open
Database Connectivity, provides easy connection to database
server.
• Client/Server applications
– Database applications, web applications, other applications.
Database Application
• An organized set of menus, forms, reports,
business rules, and the database it operates
on.
• An example:
– C:\Program Files\Microsoft
Office\Office\Samples\Northwind.mdb
Three components in a database
application
• Presentation – user interface
– Menus, forms, reports, etc
• Processing logic
– Business rules
• Database
Categories of Database
Applications
• One-Tier
– Legacy online transaction processing
– PC database application
• Two-Tier client/server
– Client-based presentation.
– Processing logic is buried either inside the user
interface on the client or within the database on the
server, or both.
• Three-Tier, N- tier
– Processing logic is separated from the interface and
database.
Two-Tier
• Simplicity
• Provides a basic separation of tasks. The
client is primarily responsible for the
presentation of data to user, and the server is
primarily responsible for supplying data
services to the client.
• Fat client
• Fat server
Fat Client
• More functions are placed on the client
– Presentation and processing are placed on the
client
– Traditional database/file server applications
– Decision support and personal software (enduser support)
Fat Server
• More functions are placed on the server.
– Processing logic is placed on the server
– Mission-critical transaction systems, and web
server are examples
Scalability
• The ability to add or remove clients.
• Two-tier model prevent the scalability:
– A fat client requires considerable resources on
the client computer including disk space, RAM,
and CPU power.
– A significant client-site administration
overhead.
Three-Tier
• 1. User interface, 2. Business logic and data
processing layer, 3. Database server.
• Advantage:
– Less expensive client hardware.
– Application maintenance is centralized. No software
distribution problem.
– Load balancing is easier with the separation of the
business logic from the database functions.
– Fit naturally to the web environment.
Partitioned application and
Component
• An application designed to run on a distributed system is
referred to as a partitioned application.
• A partition application consists of several parts, and each
part perform a specific and well-defined task.
• Each part of the partitioned application is referred to as a
component
• A component interacts with others via interface: properties,
methods, and events supported by the component
Interoperability between Components
• To provide seamless object integration and
allow functional components that provide
specific services to be created and plugged
from one application to another.
Microsoft’s COM, and DCOM
• Component objects: Objects that provide services
to other client applications.
• Component Object Model consists of a
specification that defines the interface between
objects and an implementation packaged as a
Dynamic Link Library (DLL).
• DCOM extends COM to distributed environment.
It allows components to look the same to clients
on a remote computer as on a local computer.
Object Management Group’s
ORB
• Object Request Broker is a distributed
software bus that enables objects to make
and receive requests and response from a
provider. On receipt of a response from the
provider, the ORB translates the response
into a form that the original requester can
understand.
Benefits of Building Applications
from Components
• Reusability
– Many applications can share the services provided by the
same component.
• Manageability
– By dividing a program into components, a project can be
divided into smaller, more manageable tasks, and each
individual programmers can build components for which
their skills are best suited.
• Maintenance
– Each component can be maintained as an individual unit.
• Flexibility
– Components are not bound to a physical location, and can
be redistributed to other physical location.
Progression of the Internet
• Hypertext web
– Publishing static web pages
– A two-tier client/server application
• Simple response web – Dynamic web pages
– Forms and three-tier CGI Common Gateway Interface
client/server
– Stateless, cookies(server data held on the client)
– Maintain session with server side scripts, ASP, JSP
– Require web server to mediate between objects running on
the client and objects running on the server.
• Object web
– Web server and object server
– Provides object- to –object interactions between client
object and server object.
The Web as a Database Application Platform
• Three-tier architecture
– Browser, web server, database server
• Advantages:
– Cross-platform support
– Graphical user interface
The Web as a Database Application Platform
• Disadvantages
– Reliability: Internet is unreliable and slow.
– Security
– Cost: hardware and software 20%, marketing
24%, content development 56%.
– Potentially enormous peak load.
– Performance:
• Interpreted languages: HTML, VBScript, JavaScript
Approaches to Integrating the Web and
DBMSs
• Common Gateway Interface (CGI)
• JAVA 2 Platform
• Microsoft Platform
CGI
• The Common Gateway Interface defines how
scripts communicate with web servers.
• A CGI script is any script designed to accept and
return data that conforms to the CGI specification.
• Processes:
– The user calls the CGI script by clicking a link or a
button.
– The server ensures the requester has access to the
script, prepares environment variables and launches the
script.
– The script executes and reads the environment variables
and STDIN and sends the output to STDOUT.
– The server sends the data in STDOUT to the browser.
Advantages and Disadvantages of CGI
• Advantages:
– Simplicity and language independence.
• Disadvantages:
– Communication between a client and the database
server must always go through the web server.
– Lack of transaction support due to the statelessness of
HTTP.
• The database server must perform the same logon and logout
for every query submitted by the same user.
Java 2 Platform
• Presentation Tier:
– JavaScript, Java applet
• Server site scripting:
– Servlets and Java Server Pages
• Business tier:
– Enterprise Java Beans (EJB): A standard for building
server-site components in Java.
• Database access:
– JDBC
– SQLJ: Static embeded SQL in Java.
Portability
Java: Write Once Run Anywhere
Java Byte Code
Java Source Code
Java Virtual Machine
(JVM)
Java Byte Code
(Intermediate Code)
Executable Code
Microsoft Platform
• Presentation Tier:
– VBScript, JScript
• Web server and Server site scripting:
– Internet Information Server, Active Server Pages
• Business tier:
– COM ActiveX components
• Database access:
– ODBC: An interface to access relational databases.
– OLE DB: An interface to access any data sources
including relational and non-relational databases, email,
text and graphics, etc.
– ADO.NET
Microsoft’s .Net
• Language must compliance with Common
Language Specification, CLS.
• Compile the language into Microsoft Intermediate
Language (MSIL) code.
• The MSIL code is then executed in the
Common Language Runtime (CLR), which
conceptually is same as the JVM, where it is
translated into machine code by a compiler.
Techniques Covered in BICS546
• Prerequisites: Programming, Database, SQL
• Visual Basic .NET
– Interface and event-driven programming
– Class and component programming
• Database programming
– ADO.NET programming model
• Web Techniques:
– Client side scripting
• Browser object mode, VbScript, JavaScript, HTML
– Server side scripting: ASP.NET
• XML