systems architecture: client/server systems naim r. el-far, phd candidate ta for seg3202 software...

Systems Architecture:

Client/Server Systems

Naim R. El-Far, PhD Candidate

TA for SEG3202 Software Design and Architecture with N. El-Kadri (Summer 2005)

Tutorial 1 of 4 – 27/5/2005

Friday 27/5/2005Naim R. El-Far2

About Me

Naim R. El-Far PhD Candidate DISCOVER Lab @ SITE Email: [email protected] Please always start your email subject line

with the course code (SEG3202) Office: SITE 5-077 (DISCOVER Lab). Office Hours: None scheduled. By

appointment only.


About Today’s Material

Slides based on presentations by N. El-Kadri of the University of Ottawa (http://www.site.uottawa.ca/~nelkadri) and Dr. D. Penny of the University of Toronto (http://www.cs.toronto.edu/~penny).

Material also from the Carnegie Mellon Software Engineering Institute web site (http://www.sei.cmu.edu).


Tutorial Outline

1. A Re-introduction to Software Engineering2. The Software Engineering Process: Architecture vs.

Design3. Classification of Software Architectures

1. Monolithic2. Client/Server3. N-tiered

4. Introduction to Client/Server Architectures5. Examples of Client/Server Architectures6. Division of Work in Client/Server Architectures7. Inter-Process Communications8. Quantifying Communication Performance9. A Quick Survey of Socket Programming in Java10. A Quick Survey of SQL Programming in Java


Introduction:

Software Engineering

In the context of engineering a sizable software project:

Plan your work, and work your plan. Modifications along the way are

inevitable, but the more work you put in planning out the project up front, the more likely the project would go smoothly.


Introduction:

Software Engineering (cont.)

This is what software engineers do! More formally, IEEE defines software

engineering as: “The application of a systematic, disciplined,

quantifiable approach to the development, operation, and maintenance of software”.

To be systematic, disciplined, and able to quantify our work, we need to …

classify, categorize, and divide into modules!


Introduction:

Software Engineering Process

The Software Engineering process, is twofold:

1. Make decisions regarding the systems-level architecture.

2. Implement and perform programming-level design.


Introduction:

Software Engineering Process (cont.)

The concept of Architecture

vs The concept of Design

1. Strategic

2. High-level decisions about the system structure and components

3. System-scope

1. Tactical

2. Programming-level decisions about how to implement the architecture

3. Component(s)-scope


Introduction:

Software Engineering Process (cont.)Architecture and design in the development process:


Introduction:

Software Architecture Definition

How do we formally define Software Architecture?

(SEI) Structure or structures of the system, which consists of software components, the externally visible properties of those components, and the relationships among them.


Introduction:

Software Architecture Design

What do software architecture decisions involve?Specifying at the highest level the construction of the system: Technology choices

• Platforms, language, database, middleware, etc System construction

• How can we best construct the system logically and physically

• Hardware interfaces (if any) Division into programs

• E.g. a program for data entry, another for data analysis, a Web-oriented interface, etc.

Division of programs into major subsystems• Reuse strategy (shared subsystems)• Calls constraints• Major strategies (e.g., for persistence, IPC, etc.)


Introduction:

Software Architecture Classification

How do we classify different software architectures? Convention is to classify based on number of

conceptual/physical layers running the software components.

In other words, a tier-based system:1. 1-tier software architectures: Aka Monolithic systems

(from the Greek mono-lithos, or single rock), e.g. word processors, PowerPoint, and stand-alone applications.

2. 2-tier software architectures: Aka Client/Server systems, e.g. Internet browsers, large database systems, etc.

3. N-tier software architectures: Systems that have 3 or more layers as described above, e.g. complex business and banking databases.


Introduction:

Software Architecture Classification (cont.)Monolithic architecture example: Payroll for a small businessScenario: Small business with 1 location 5 Employees Single computer (computer A) with local database

containing each employee’s hourly rate and number of hours worked.

John’s pay (calculated on A) = John’s hourly rate (stored on A) x the number of hours John worked (stored on A)

But what if the business grows and now has several locations and tens of employees?


Introduction:

Software Architecture Classification (cont.)

Monolithic architecture


Introduction:

Software Architecture Classification (cont.)Server/Client architecture example: Payroll for a large businessScenario: Large business with 6 locations and 80 employees. 4 locations share a single employee database (stored on server A)

while the other 2 share another database (stored on another geographically distant server B)

Payroll report generated at business headquarters at a third location on computer C.

John’s Pay (calculated on C) = John’s hourly rate (stored on A) x the number of hours John worked (stored on A)

Computer C is a client computer that requests information from server A. A “client” requests, and a “server” serves, hence client/server architecture.

But what if the business goes multinational and calculating payroll becomes different from one employee to another?


Introduction:


Client/Server architecture


Introduction:

Software Architecture Classification (cont.)N-tier (N=3) architecture example: Payroll for a large multinational businessScenario: Large business with 400 employees in 2 different countries: Canada and

France. Full work week in Canada is 40 hours, but in France is 35 hours. Overtime in Canada is calculated at 1.5 times the hourly rate, but in France

it is 1.3 times the hourly rate. Different deductions in Canada than those in France. More “business rules”. To calculate payroll in a client/server architecture, we will need to modify the

rules at the client level for each client. If we introduce a middle-tier to host all “business rules” then all client

requests can be standardized, and all database schemas can remain independent (in that they are not affected by changes in the client or middle-ware software). The middle-tier will take care of everything else.


Introduction:


3-tier architecture


Introduction:


Today’s emphasis is on the

Client/Server Architecture


Client/Server Architecture:

Introduction

How do we formally define the client/server software architecture?(SEI) The client/server software

architecture is a versatile, message-based and modular infrastructure that is intended to improve usability, flexibility, interoperability, and scalability.



Introduction

In general, any application where multiple clients connect to a single server.

client1 client2 client3

server



Introduction

Worth noting, client/server systems were not the first response to the inadequacy of monolithic systems.

Before, there was:

1. The Mainframe (dumb terminal/ smart mainframe) architecture, and

2. The File-Sharing (smart desktop/dumb storage) architecture.



Examples Relational Database Management System (RDBMS)

Most common client/server program is where the server is a relational database server.

Warning: some use the term client/server to refer to this usage exclusively.

RDBMS




Examples (cont.)

RDBMS Implementation

disks


RDBMS Server



Division of Work

Mainframe architecture: dumb client (terminal), overworked smart server (mainframe).

File-sharing architecture: smart but irresponsible client (terminal), dumb server (networked storage device).

Client/Server architecture: smart client, smart server.



Division of Work (cont.)Client machine’s typical responsibilities:

Manage the user interface (typically a GUI) Manage the interface with the operating

system (and by extension, system resources)

Validate data before communicating with server

Communicate with server (send/receive) Some logic (depending on the application)



Division of Work (cont.)Server’s typical responsibilities:

Listen for and receive requests from clients

Process the request enforcing all relevant logic

Respond to client



Inter Process CommunicationsQ) How do the clients/servers and

clients/servers communicate (Inter-Process Communication – IPC)?

Remember, client/server architectures must respect the heterogeneity of their components and the need for their interoperability.

A1) How about memory sharing?• Makes no demands on heterogeneity and

interoperability• Very fast!• Not ideal for networks



Inter Process Communications (cont.)A2) How about message passing?

• Preserves heterogeneity and interoperability (if standardized)

• Not as fast as shared memory but if standardized correctly, fast enough

• Ideal for networks

Common protocols for IPC in Client/Server architectures:

1. Socket (Transmission Control Protocol - TCP, User Datagram Protocol - UDP)

2. Remote Procedure Calls – RPC3. Distributed Objects - DO



Quantifying Communication PerformanceRemember, Software Engineering is

““The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software”.

We’ve so far been systematic and disciplined in our approach. We’ve have nothing to quantify really, until now.



Quantifying Communication Performance (cont.)How fast you get information

(communication speed) is two-fold (disregarding monetary cost for the moment):

1. How much information you can get at a time (bandwidth), and

2. How long it will take to get more information (latency).



Quantifying Communication Performance (cont.)Concorde:

100 passengers (low bandwidth), 3 hour London to New York flight time (low latency).

Boeing 747:

500 passengers (high bandwidth), 8 hour London to New York flight time (high latency)



Quantifying Communication Performance (cont.)Q) How do we formally define bandwidth (in

the context of quantifying communication performance)?

A) The amount of data that can be transferred through a digital connection in a given time period (i.e., the connection's bit rate). In such cases, bandwidth is usually measured in bits or bytes per second.



Quantifying Communication Performance (cont.)List of common connection bandwidths:

Device Bandwidth

56k Modem 53.3 kb/sec

128k ISDN 128 kb/sec

USB Full-Speed 12 Mb/sec

Bluetooth 2 3 Mb/sec

T1 1.54 Mb/sec

Ethernet 10 Mb/sec

Gigabit Ethernet 1 Gb/sec



Quantifying Communication Performance (cont.)

How accurate are these bandwidth numbers?

If we send a large file on a round-trip through a connection medium, then chances are, it’ll come back later than the theoretic values in the table predict.



Quantifying Communication Performance (cont.)Q) How do we formally define latency (in the

context of quantifying communication performance)?

A) The time it takes for a given message to make a “round-trip” to a given destination in a network.

Throughput: the observed bit rate as opposed to bandwidth, which is the theoretic bit rate.

Throughput < Bandwidth because of overhead.



Quantifying Communication Performance (cont.)

Balancing Bandwidth and Latency: What does you application need more? A

“Concorde” or a “747 Jumbo jet”? Satellite communication (16 Mbits/sec for

Internet) but 1 – 2 sec latency: Bad for online gaming, great for TV broadcast.



Quantifying Communication Performance (cont.)Given that typically local communication has bandwidth

several orders of magnitude greater than network communication, and has latency several orders of magnitude less than network communication:

1. Limit network communication as much as possible (i.e. do as few calls as possible remotely)

2. Preference given to asynchronous protocols3. Larger transactions4. Communication should maximize data while

minimizing frequency of communication.



A Quick Survey of Socket Programming in Java Good introductory tutorial available at

http://www.javaworld.com/javaworld/jw-12-1996/jw-12-sockets.html

Again, a socket is an IPC channel identified uniquely by a port number and an IP address

Programming paradigm: Traditional stream open read/write close, just like file I/O



A Quick Survey of Socket Programming in Java (cont.) Socket programming can use two

communication protocols:

1. UDP/IP: User Datagram Protocol over Internet Protocol. Connectionless and does not guarantee delivery.

2. TCP/IP: Transmission Control Protocol over Internet Protocol. Establishes a connection, then streams data guaranteeing sequential delivery.



A Quick Survey of Socket Programming in Java (cont.)Client side: Opening a socket:

Socket MyClient;try {

MyClient = new Socket("Machine name", PortNumber);

}catch (IOException e) {

System.out.println(e);} Port number should be greater than 1023. (20 for FTP data, 21

for FTP control, 53 for DNS, 80 for HTTP, 110 for POP3, 443 for HTTPS, 569 for MSN)



A Quick Survey of Socket Programming in Java (cont.)Server side: Opening a socket:

ServerSocket MyService;try {

MyServerice = new ServerSocket(PortNumber);}catch (IOException e) {

System.out.println(e);}

We also need a socket to listen to and accept requests from clients:

Socket clientSocket = null;try {

serviceSocket = MyService.accept();}catch (IOException e) {




A Quick Survey of Socket Programming in Java (cont.)

Client side: Opening an input stream:DataInputStream input;try {

input = new DataInputStream (MyClient.getInputStream());

}catch (IOException e) { System.out.println(e);}




Server side: Opening an input stream:DataInputStream input;try {

input = new DataInputStream(serviceSocket.getInputStream());

}catch (IOException e) { System.out.println(e);}




Client side: Opening an output stream:PrintStream output;try {

output = new PrintStream(MyClient.getOutputStream());

}catch (IOException e) {System.out.println(e);}




Server side: Opening an output stream:PrintStream output;try {

output = new PrintStream(serviceSocket.getOutputStream());






Client side: Closing the sockets:try {

output.close();input.close();MyClient.close();






Server side: Closing the sockets:try {

output.close();input.close();serviceSocket.close();MyService.close();

} catch (IOException e) {




A Quick Survey of SQL Programming in Java

SQL: Structured Query Language. A standard language for querying and modifying relational databases

Very intuitive (although database relations can become a little convoluted)



A Quick Survey of SQL Programming in Java (cont.)SELECT * FROM employees WHERE DeptID=3

INSERT INTO supplier(supplier_id, supplier_name)VALUES (24553, 'IBM')

DELETE FROM supplierWHERE supplier_name = 'IBM';



A Quick Survey of SQL Programming in Java (cont.)Java programs running on client machines

need a way (an API or middleware) to communicate with the SQL engine running on the server machine

Enter JDBC: Java Database Connectivity. JDBC is a Java API that enables Java programs to execute SQL statements. This allows Java programs to interact with any SQL-compliant database.

Note: Open Database Connectivity (ODBC) and its up and coming successors are the non-Java alternative.



A Quick Survey of SQL Programming in Java (cont.)import java.sql.*;public class Main {

private static final query = “select itemname,quantity “ + “from orderitems,items “ + “where orderid=1 and orderitems.itemid=items.itemid”;

public static void main(String[] args) throws Exception {Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");Connection c = DriverManager.getConnection("jdbc:odbc:grocery");Statement s = c.createStatement();if( s.execute(query) ) { ResultSet r = s.getResultSet(); printResults(r);

} }

private static void printResults(ResultSet r) throws Exception { final int nC = printHeadings(r); printRows(nC, r); } …}


Recap

Software engineering is simply applying engineering concepts to the software lifecycle.

System-level architecture (1-tier, 2-tier, 3-tier, platforms, languages, hardware, etc) and programming-level design (OO, procedural, logical, data structures, etc)

Client/Server architecture in-depth: physical and logical layers, division of work, inter-process communication

Communication metrics: speed, latency, bandwidth, and throughput

Java socket programming in client/server architecture Java interfacing with SQL-based RDBMS

systems architecture: client/server systems naim r. el-far, phd candidate ta for seg3202 software...

Documents

software engineering

software components

maintenance of software

software engineers

seg3202 software design

sizable software project

clientserver systems

systems architecture