Chapter 10 - System Architecture

Learning Objectives

• Provide a checklist of issues to consider when selecting a system architecture
• Trace the evolution of system architecture from mainframes to current designs
• Explain client/server architecture
• Describe the impact of the Internet on system architecture
• Compare in-house e-commerce development with packaged solutions and service providers
• Explain online and batch processing
• Describe network models, including hierarchical, bus, ring, star, and mesh topologies
• Explain network devices, including routers, gateways, and proxy servers
• Describe wireless networking, including wireless standards, topologies, and trends
• Explain the final activities in the systems design phase

Architecture Checklist

Issues that influence architecture choice:

• Corporate organization and culture
• Enterprise Resource Planning (ERP)
• Initial and Total Cost of Ownership (TCO)
• Scalability
• Web integration
• Legacy system interface requirements
• Processing options
• Security issues
• Corporate portals

Corporate Organization and Culture

• A successful system performs well in a company's organization and culture
• The architecture must align with how the business actually operates

เหมือนกับการเลือกแบบบ้าน ต้องดูก่อนว่าครอบครัวใหญ่หรือเล็ก อยู่แบบไหน ถึงจะออกแบบได้พอดี

Enterprise Resource Planning (ERP)

• Objective: Establish a company-wide strategy for using IT that includes:
  • A specific architecture
  • Standards for data, processing, network, and user interface design
• Companies extend internal ERP systems using Supply Chain Management (SCM)

ERP = พิมพ์เขียวกลางของบริษัท ทุกระบบต้องเล่นตามกติกาเดียวกัน

Initial Cost and TCO

• TCO (Total Cost of Ownership) includes:
  • Tangible purchases, fees, and contracts → called hard costs
• TCO analysis answers questions about:
  • Validity and effectiveness of the system
  • New trends in systems planning
  • Impact on initial cost for a proposed system

TCO ไม่ใช่แค่ราคาซื้อ แต่รวมค่าดูแล ค่าอัปเกรด ค่าพนักงานทุกอย่างด้วย

Scalability (Extensibility)

• System's ability to expand, change, or downsize easily to meet changing needs of an enterprise

เหมือน SwiftUI layout ที่ adaptive — ขยายหรือย่อได้โดยไม่ต้อง rewrite ทั้งหมด

Web Integration

• Web-centric architecture enables a company to integrate new applications into its e-commerce strategy
• New systems should be designed with web connectivity in mind

Legacy Systems

• A new system might have to interface with legacy systems
• Involves analysis of:
  • Data formats
  • Compatibility between old and new systems

Legacy system = โค้ดเก่าที่ยังต้องใช้งานอยู่ ต้องหา adapter ให้มันคุยกับระบบใหม่ได้

Processing Options

• Systems can process data online or in batches
• (Covered in detail in Processing Methods section)

Security Issues

• Analysts must consider security issues and how the company will address them
• Security must be built into the architecture from the start, not added later

Corporate Portals

• Provide access for customers, employees, suppliers, and the public
• Integrates with various other systems
• Provides a consistent look and feel across organizational divisions

The Evolution of System Architecture

Functions of a Business Information System

• Manage applications that perform processing logic
• Handle data storage and access
• Provide an interface that allows user interaction

While planning system design:

• Determine where each function will be carried out
• Identify the advantages and disadvantages of each design approach

Mainframe Architecture

• Server: A computer that supplies data, processing services, or other support to one or more computers called clients
• Earliest servers were mainframe computers
• Advances in technology enabled installation of terminals at remote locations

Mainframe ยุคแรก = ห้องเซิร์ฟเวอร์ใหญ่หนึ่งห้อง ทุกคนต่อ terminal เข้ามา ไม่มี logic อยู่ที่ client เลย

Impact of the Personal Computer

• Individuals could work in stand-alone mode
• Lesser IT assistance resulted in increased productivity in certain tasks
• Shifted some computing power away from centralized servers to individual machines

Network Evolution

• LAN: Connects devices like printers, scanners, and computers within a building or campus
• WAN: Interconnects multiple LANs across cities, countries, or continents

💻 Client/Server Architecture

• Systems divide processing between one or more networked clients and a central server
• Client handles the entire user interface
• Server stores data and provides data access and database management functions

เหมือน iOS app — iPhone (client) ทำ UI, backend server เก็บ database ไว้

The Client's Role

Client/Server Tiers

Two-Tier Design

• User interface resides on the client
• Data resides on the server
• Application logic can run on the server, client, or divided between both

Three-Tier (n-Tier) Design

• User interface runs on the client
• Data is stored on the server
• Has a middle layer (Application Server) between the client and server
• The middle layer handles business logic separately from both UI and data

Three-tier = MVC architecture บน iOS — View (client), Controller/ViewModel (app server), Model/Database (data server)

Middleware

• Enables communication between tiers
• Also called "glueware"
• Connects two or more software components in a federated system architecture

Cost-Benefit Issues

• Client/server systems offer the best combination of features to meet information system requirements
• Must weigh upfront hardware/software cost vs. long-term flexibility

Performance Issues

• Knee of the curve: Response time to requests increases significantly as the system nears its capacity
  $\boxed{\text{Response Time} \uparrow \text{ sharply as load} \to \text{capacity}}$
• Client should contact the server only when necessary
• DDBMS (Distributed Database Management System) helps improve client/server performance

Knee of the curve เหมือน Bangkok traffic — ถนนรับได้ถึงจุดนึง พอเกินนั้นปุ๊บ ติดเต็มทันที

The Impact of the Internet

Internet-Based Architecture

• Entire user interface is provided by the web server in the form of HTML documents
• Shifting responsibility for the interface from client to server:
  • Simplifies data transmission
  • Results in lower hardware cost and complexity

Cloud Computing

• Refers to the cloud symbol often used to represent the Internet
• Envisions a cloud of remote computers providing a total online software and data environment, hosted by third parties
• Key advantages:
  • Eliminates compatibility issues
  • Provides scaling on demand

Cloud = ไม่ต้องซื้อเซิร์ฟเวอร์เอง ใช้ของ AWS/GCP แล้วจ่ายตามที่ใช้จริง เหมือนจ้างคนขับแทนการซื้อรถ

Web 2.0

• Second generation of the web
• Enables people to collaborate, interact, and share information more dynamically
• Considered a step towards the semantic web
• Wiki: Web-based repository of information run by social collaboration
• Users collaborate and add new layers of information to the Internet operating system

E-Commerce Architecture

In-House Solutions

Benefits:

• A unique website with a look and feel consistent with the company's other marketing efforts
• Complete control over the organization of the site
• A scalable structure to handle increases in sales and product offerings in the future
• More flexibility to modify and manage the site
• Opportunity to integrate the firm's web-based business systems with its other information systems

Packaged Solutions

• Viable alternative for medium- to large-sized firms
• Less complex to implement compared to in-house development
• Trade-off: less customization flexibility

Service Providers

• ASP (Application Service Provider): Provides applications or access to applications by charging a fee
• Many offer full-scale Internet business services for companies that decide to outsource functions

Processing Methods

Online Processing

• Online systems handle transactions when and where they occur
• Output is provided directly to users
• Advantages:
  • Avoids delays
  • Allows a constant dialog between the user and the system
  • Can be used with file-oriented systems

Example — ATM Query Process:

Step 1: Customer enters account number and requests balance
Step 2: System retrieves current account balance from Customer File
Step 3: Verifies bank account number and displays balance on ATM screen

Online processing = ถามปุ๊บ ได้คำตอบทันที เหมือนเรียก API แบบ synchronous

Batch Processing

• Data is managed and processed in groups
• Advantages:
  • Tasks can be planned and run on a predetermined schedule without user involvement
  • Programs requiring major network resources can run when costs and impact on other traffic will be lowest
  • Well-suited to address security, audit, and privacy concerns

Example — POS (Point of Sale) Terminals:

POS Terminal → POS Program (Online) → Sales Transaction File → Daily Sales Program (Batch) → Daily Sales Report
                        ↕                                                    ↕
                   Inventory                                         Accounting Files

• Online part: Retrieves item data, updates quantity in stock, produces transaction record
• Batch part: End of day — produces daily sales report and updates accounting system

Batch = การบ้านที่ส่งทีเดียวตอนเย็น ไม่ต้องส่งทีละข้อตลอดวัน เหมือน cron job ที่รัน background

Network Models

OSI Model (Open Systems Interconnection)

• Describes how data moves from an application on one computer to an application on another networked computer
• Provides physical design standards that assure seamless network connectivity, regardless of the specific hardware environment

Network Topology

• Physical topology: Actual network cabling and connections
• Logical topology: Describes the way the components interact

Hierarchical Network

• Departmental servers control lower levels of processing and network devices
• Tree-like structure with network server at the top

Bus Network

• A single communication path connects the central server, departmental servers, workstations, and peripheral devices
• All devices share one common line

Ring Network

• Resembles a circle where data flows in only one direction from one device to the next
• Token-passing method commonly used

Star Network

• Has a central networking device called a switch which:
  • Manages the network
  • Acts as a communications conduit for all network traffic
• Most common modern LAN topology

Mesh Network

• Each node connects to every other node
• Provides a high degree of redundancy
• Used in military and mission-critical applications
• Provides alternate data paths, but is expensive to install and maintain

Mesh = เหมือน internet backbone — ถ้าเส้นนึงพัง ยังมีทางอื่นให้ข้อมูลวิ่งไปได้

Network Devices

• LANs or WANs can be interconnected using:
  • Router: Connects network segments, determines most efficient data path, and guides flow of data
  • Proxy Server: Provides Internet connectivity for internal LAN users
• Gateway: Created by routers to bridge between different network topologies and large, dissimilar networks (e.g., the Internet)

Router = ไปรษณีย์ — รับจดหมาย (packets) แล้วหาเส้นทางที่เร็วที่สุดไปส่ง

Wireless Networks

Standards

• IEEE 802.11 is a family of standards developed by the Institute of Electrical and Electronics Engineers (IEEE) for wireless LANs
• Current wireless networks are based on variations of the original 802.11 standard
• MIMO (Multiple Input/Multiple Output) technology boosts performance by using multiple antennas

Topologies

Network topologies available for IEEE 802.11 WLANs:

• BSS (Basic Service Set) — also called infrastructure mode: Devices connect through a central Access Point (AP)
• ESS (Extended Service Set): Multiple BSSs connected together, extending the wireless coverage area

Trends

• Wi-Fi Alliance:
  • International association that certifies interoperability of wireless network products based on IEEE 802.11 specifications
  • Products with Wi-Fi certification are guaranteed to work together
• Bluetooth:
  • Used for short-distance wireless communication
  • Typically within ~10 meters range

System Design Completion

System architecture marks the end of the systems design phase of the SDLC.

Final Activities in the Systems Design Phase

1. Preparing a system design specification
2. Obtaining user approval
3. Delivering a presentation to management

System Design Specification

• A document that presents the complete design for a new information system
• Contains:
  • Detailed costs
  • Staffing requirements
  • Scheduling for completing the next SDLC phase
• Used as a baseline to measure the operational system

Sections in a System Design Specification:

• Management summary
• System components
• System environment
• Implementation requirements
• Time and cost estimates
• Additional material

User Approval

• Users must review and approve:
  • Interface design
  • Report and menu designs
  • Data entry screens
  • Source documents
  • Other areas that affect them
• Benefits:
  • Ensures approvals are obtained as and when required
  • Keeps the users involved with the system's development
  • Provides feedback that can be used to guide efforts
• System design specification should also be reviewed by other IT department members

Presentations

Three-stage presentation process:

• Provide an opportunity to:
  • Explain the system
  • Answer questions
  • Consider comments
  • Secure final approval
• Management will reach a decision based on the final presentation

Summary

• An information system combines hardware, software, data, procedures, and people into a system architecture
• Before selecting an architecture, the analyst must consider: ERP, initial cost and TCO, scalability, web integration, legacy interface requirements, processing options, security issues, and corporate portals
• ERP establishes an enterprise-wide strategy for IT resources and specific standards
• Client/server architecture divides processing between one or more clients and a central server
  • Thick client → processing logic at the client
  • Thin client → processing logic at the server
  • Can be two-tier or three-tier
• The Internet has had an enormous impact on system architecture (cloud, Web 2.0)
• The most prevalent processing method today is online processing
• Network topologies: hierarchical, bus, ring, star, mesh
• The system design specification presents the complete design and is the basis for the presentations that complete the systems design phase