CS125 Midterm Lecture 1 - Software or System Architectures

8/7/2019 CS125 Midterm Lecture 1 - Software or System Architectures

1/35


2/35

Lecture ObjectivesLecture ObjectivesSoftware/System Architecture

0 After this lecture, the student should be able:

0 define software architecture,0 describe the types software architecture, and

0 learn basic elements of each type software

architectures.


3/35

What is Software/System Architecture?Software/System Architecture

0Organization of the overall system.

0Serves as the outline for both the system and theproject developing it, defining the workassignments that must be carried out by design andimplementation teams.

0Product for early analysis to make sure that the

design approach will yield an acceptable system.0Conceptual glue that holds every phase of the

project together for all its many stakeholders.


4/35

Fundamental Attributes ofa Quality

ArchitectureSoftware/System Architecture

0Robust. Architecture changes can be performedwithout disturbing the entire architecture.

0 Stability. Architecture can survive for a significantperiod of time.

0 A stable and robust architecture will allow for changesbut basically remain the same over time.

0Flexibility. Architecture must allow the exchange ofexisting elements and the integration of new elementswithout major efforts.


5/35

Layers ofa Business Information SystemSoftware/System Architecture

0 Information Systems (IS) are usually built on

databases. Preparing access to the database and

accessing the database comprises a significant portionof an information system's code.

0 Presentation Layer/Tier

0

Business Logic or Application Layer/Tier0 Database Layer/Tier


6/35

Figure 1. Layers of a Business Information System


7/35

Common Types of Software/System


0 Stand-Alone Architecture (PC with Stand-alone DB)

0 File-Server Architecture

0 Client-Server Architecture (Database-Server)

0 nth-Tier Architecture0 Single tier (1-tier)

0 Dual tier (2-tier)0 Triple tier (3-tier)

0 nth-tier


8/35



0 Stand-Alone Architecture

0 Database (or files) reside on a PC - on the hard disk.0 Applications run on the same PC and directly access the

database. In such cases, the application is the DBMS.

0 Business rules are enforced in the applications runningon the PC.

0 Single user accesses the applications.


9/35

0File - Server Architecture

0All processing is done at the PC that requested thedata.

0Entire files are transferred from the server to theclient for processing.

0Problems with this architecture are:

0Huge amount of data transfer on the network

0Each client must contain full DBMS0heavy resource demand on clients

0client DBMSs must recognize shared locks, integritychecks, etc.




10/35

Figure 2.Typical File-Server Architecture Layout


11/35

0PCs are connected to a local area network(LAN).

0A single file server stores a single copy of thedatabase files.

0Applications run on each PC on the LAN andaccess the same set of files on the file server.The application is also the DBMS.


Architecture

Software/System Architecture


12/35

0Business rules are enforced in the applications

and also the applications must handle

concurrency control possibly by file locking.

0Each user runs a copy of the same application

and accesses the same files.

0e.g. Sharing MS Access files on a file server.


Architecture



13/35

0Advantages:

0 (limited) Ability to share data among several users

0 Costs of storage spread out among users0 Most components are now commodity items - prices

falling

0Disadvantages:

0 Limited data sharing ability - a few users at most


Architecture



14/35

0Client-Server Architecture

0Architecture that was developed as a

response to the limitations of file-sharingarchitectures, which require tons ofbandwidth and can often stall a networkcausing it to crash.

0Requires low shared usage and low volume ofdata to be transferred.

0Database server replaced the file server.


Architecture



15/35

0Relational Database Management Systems(RDBMSs) answered user queries directly.

Since only specific queries were beinganswered, only that data was transferredinstead of entire files that slow downnetworks.

0Improves consistency in data between users,since all users had access to the sameupdated information.


Architecture



16/35

Figure 3.Typical Client-Server Architecture Layout


17/35

0In client-server systems, typically defines thefollowing:

0 Networked computing model

0 Processes distributed between clients and servers

0 Client Workstation (usually a PC) that requestsand uses a service

0 Server Computer (PC/mini/mainframe) thatprovides a service

0 For DBMS, server is a database server


Architecture



18/35

Figure 4. Application Logic in Client-Sever Systems


19/35

Tiers we are going to

study

Figure 5.Evolution of nth-

Tier Architecture


Architecture



20/35

0Single-Tier Architecture

0Time of huge mainframe

0All Processing in single computer

0All resources attached to the same computer

0Access via dumb terminals


Architecture



21/35

Figure 6. Layout of single-tier database architecture


22/35

0Advantages

0 Simple

0 Efficient0 Uncomplicated

0Disadvantages

0 Very Expensive


Architecture



23/35

0Two-Tier Architecture

0 Consist of three components:

0User system interfaces,

0Processing management, and

0

Database management.


Architecture



24/35

0 User System Interf ace (USI) - is a component of an

organizations decision support system, which includes human

decision-makers. It provides a user friendly layer of

communication to make requests of the server and offersmultiple forms of input and output. USIs include features like

display management services, sessions, text input, and dialog.

0 Processing Management - includes process development,

process implementation, process monitoring, and processresources services.

0 Database Management- includes database and file services.


Architecture



25/35

0 Derives its name from how it distributes workbetween clientand server.

0 Clients access databases through the user system interface.

0 Database management, on the server side, distributesprocessing between both client and server.

0 Both tiers (client and the server) are responsible for some ofthe processing management.

0 Thin client is a PC just for user interface and a littleapplication processing. Limited or no data storage(sometimes no hard drive)


Architecture



26/35


27/35

0Clientis responsible for

0I/O processing logic

0Some business rules logic

0Server performs all data storage and accessprocessing

0 DBMS is only on server


Architecture



28/35

0Advantages:0 Clients do not have to be as powerful0 Greatly reduces data traffic on the network0 Improved data integrity since it is all processed centrally0 Improve usability though user-friendly, form-based

interfaces.0 Improve scalability because two tiered systems can hold up

to 100 users, whereas file server architectures can onlyaccommodate 12.

0 best suited to homogeneous environments for processing

non-complex, non-time sensitive information.

0Disadvantages:0 Expensive0 File server limited only to 12 users.


Architecture



29/35

0Three-Tier Architecture

0Applications runs on the traditional client-

server model but from a application server.

0Client only displays the GUI and data, but has

no part in producing results

0Database server serves to few connections


Architecture



30/35

Figure 8. Application logic in three-tier database architecture


31/35

31

Thin clientsThin clients

BusinessBusinessrules onrules onapplicationapplicationserverserver

DBMS onlyDBMS only

ononDatabaseDatabaseserverserver


32/35

0Advantages:

0 Scalability

0 Application Servers can be deployed on many machines0 Database no longer requires a connection from every client.

0 Reusability0 If a standard object is employed, the specific language of

implementation of middle tier can be made transparent.

0 Data Integrity0 The middle tier can ensure that only valid data is allowed to be

updated in the database.


Architecture



33/35

0Advantages:

0 Improved Security0 Since the client doesnt have direct access to the database, Data layer is

more secure.0 Business Logic is generally more secure since it is placed on a secured

central server.

0 ReducedDistribution0 Changes to business logic only need to be updated on application

servers and need not to distributed on clients

0 Improved Availability0 Mission Critical Applications can make use of redundant application

servers and redundant application servers, so it can recover fromnetwork of server failures


Architecture



34/35

0Disadvantages:

0 Expensive

0 Increased Complexity / Effort

0 In General, 3-tier Architecture is more complex to build

compared to 2-tier Architecture.

0Point of Communication are doubled


Architecture



35/35

Client does

extensive

processing

Client does little

processing

Comparison of Software ArchitecturesSoftware/System Architecture

0 Stand-Alone Architecture

0 File Server Architecture

0 Client-Server Architecture

0 nth-Tier Architecture

Date post:	09-Apr-2018
Category:	Documents
Upload:	vsrivera
View:	220 times
Download:	0 times

CS125 Midterm Lecture 1 - Software or System Architectures

Documents