client server unit 2 continue

UNIT-II The Client The Client Hardware and Software

• Using client h/w and s/w, the user interacts   with the presentation logic. • Interacts with the app. Logic and the network   s/w on the client, which passes requests to   the server       1.Client Components       2.Client Operating Systems       3.GUI       4.X window vs Windowing       5.Database Access       6.Application Logic

1.Client Components

1.1 Client Hardware- the front end client m/c   runs s/w that is responsible for the presentation   and manipulation of data. – The client s/w generates a data request and   sends it to the server. – Client based processing app. And cooperative   processing app. Require enough memory to   lead and execute application logic – Higher processing speeds, a more powerful   chip, and memory caching will improve   response times.

1.2 Client Software   – A client m/c could be running as many as four     s/w packages as in the fig.   – Client m/c runs an OS and an interface     environment such as Window 3x,     Presentation Manager and openLook.

Possible s/w on a client m/c

1.3.Interface Environments • Accepting data request from the user, sending   those requests to the server, receiving results   data from the server and manipulating and   formatting those results according to the   requirements. • Graphical User Interface- GUI

– Information is presented in areas called windows-   small pictures, icons, click. – Drag and drop – Control features-container, notebook, .. – Stadard Dialogues- Open, Save and font changes

• Other interfaces- query and reports, and graph

2.Client Operating Systems • The most popular OS

– Micro Soft MS-DOS – IBM OS/2 – UNIX Based OS

• DOS with Windows 3.x

– Dos one disadvantage- 16 bit OS – Latest MS DOS, MS-DOS 5.0 – Windows 3.x- 3 tech boosts its applicability 1. Dynamic Link Libraries 2. Dynamic Data Exchange 3. Object Linking and Embedding

• OS/2

– OS/2 2.0 , a 32 bit OS from IBM – OS/2 2.0 simultaneously run DOS, Windows – OS/2 2.0 is multitasking OS

• UNIX Based

– Operate in a multitasking, multi user   environment – Support Single user or multiple users

3.What is a GUI?

– Graphical User Interface (GUI)- tasks displayed on the window   are chosen by pressing (clicking) a mouse button. – 3.1 Screen Characteristics – User can change the color, size and position of a window and   can open a new window                        Sample GUI Screen

• • • • • • •

Mouse events Key board events Window update events Resizing events Active/Deactive events Menu events Start/Stop events

• Event loop- Consists of an event handling   routine and a dispatcher

– Calls a specific lib routine that checks for   pending events.

Event Loop

• Event callback- event routine is calling   once for each event

Event call back

• Hybrid combines event loop model and   event callback model

X Window Vs. Windowing

• Two GUI camps. X Window- runs on UNIX   based systems. • The two major X Window environments are   Motif and OpenLook • Windowing- Windows 3.x, Presentation   Manager, Macintosh, and NeXtStep from   NeXt, Inc.

• X window GUIs- based on Client/Server   model

– Allows app. to access displays on networked   client stations

X Window System Architecture

• Windowing GUIs- Each interface has its   own look and feel and there are some   commonly available fns in each   environment. • Other Environments-DECwindows is a   GUI for Digital’s UNIX-based Ultrix and   VMS systems.

Database Access

– Data storage within client/server computing,   structured Query Language (SQL) – SQL queries are generated by the client and executed   on the server

• SQL Interface

– User accesses the data on the server depends on the   tool used to generate the interface. – User should not have to know SQL to build an sql   query – Some interfaces use graphics to lead the user   through every step of the building process. – Extended SQL- extensions may make their products   more attractive

Application Logic • Some c/s app. Simply use the front end   interface to access data.

– There is no app. Logic running on the client.

• Generated App. Logic- generate the   presentation logic for menus and forms. • Customized App. Logic

– Customized code requires a skilled   programmer/ developer.

Client Software Products

• GUI Environments

– Windows 3.x

• Strengths- powerful memory management and DDE protocol   (supports hot links between pgms). • Windows two memory pools- Local Pool, Global pool • Local pool (to the application), Global pool (Can access by   any pgm in the system)

– Dynamic Link libraries

• Coded routines to be modularized and improve the execution   performance and maintainability of an app. • Code can be packaged according to functionality and the   performance.

– Dynamic Data Exchange

• Provides automatic information exchange between   app. • Used to link a group of cells between two programs,   such as MS-Word and Excel for windows. • If a graph of the spreadsheet data is loaded into a   document and the spreadsheet numbers change, the   corresponding area of the document is automatically   updated.

– Object Linking and Embedding

• Users to build compound documents and focus on   their data (words, numbers and graphics) • A document is treated as a collection of objects, rather   than a file.See the next slide Fig.

Comparison of DDE and OLE

– Windows APIs

• Windows network interaction is the Winnet driver,   set of APIs – bridge the windows front-end with the   n/w OS. • Winnet is part of the Windows Device Driver Kit • Lan Manager uses Winnet APIs to browse network   servers. • Banyan’s StreetTalk, for Distributed database.

– Windows upgrades

• Object oriented version of Windows, code-named   cairo, released in 1994. • Cairo uses an Object File System-stores data and   application components.

– Windows new technology

• Presentation Manager

– PM has built in support for OS/2 features, such as   multitasking, dynamic link libraries and named pipes

• Motif

– To support Presentation manager – Motif’s development environment includes the following   tool – User Interface X Toolkit – User Interface Language – Window Manager

• OpenLook

– Developed by Sun Microsystems and AT&T – For inter client communications

See the next PPT

• Converting 3270/5250 Screens • Database Access Tools

– Access Point – Data workbench

• • • •

Data Entry Utilities Data Dictionary SQR (Structured Query Report Writer)

Client Requirements