CS CS 5150 Software Engineering Lecture 14 System Architecture 2

CS Administration Second assignment Everybody who presented last week should have received comments on their presentation and report. Several teams did not have a good schedule. If you are one of these teams, please create a schedule and include it with your progress report on Friday this week.

CS Administration Next and final presentations Sign up now Team members who were unable to come to the first presentation should attend the second

CS Administration Tests There are 4 tests, each with 2 questions. The final grade will be based on the best 6 questions out of 8. Uncollected answer books are at 301 College Avenue. Average grades: Test 1 Q1Test 1 Q2Test 2 Q1Test 2 Q Last time that this course was taught, poor test results were a common reason for getting a poor overall grade for the course

CS Test 2 Questions 1 (a) Theater Ticket System allows a purchaser to buy theater tickets online. In Phase 1, a purchaser will be able to either: (a) buy tickets online, or (b) change or cancel a previous order. To buy tickets online, the purchaser searches a database of events to discover which tickets are available, chooses tickets, adds them to a shopping cart, and possibly continues buying more tickets for other performances. When all items have been chosen, the purchaser provides information to pay for the tickets by credit card. The purchaser can choose to have the tickets sent by mail, or arrange to collect them at the theater on the day of the performance.

CS Test 2 Questions 1 (a) Draw a use case diagram that models the various ways in which a purchaser interacts with this system. The diagram should show a relationship to a use case, PaybyCredit, which models credit card payments. Definition from Lecture 9: A use case is a a task that an actor needs to perform with the help of the system.

CS Test 2 Questions 1 (a) Authenticate TakeExam > CheckGradesExamTaker Example from Lecture 9:

CS Test 2 Questions 1 (a) Example from Wikipedia:

CS Test 2 Questions 1 (a) FAQ about Use Cases See: mu.edu/course/ /umlucdfaq.html

CS Test 2 Questions 1 (a) Simple Solution BuyTickets Purchaser PaybyCredit > Change > Cancel > These could be combined

CS Test 2 Questions 1 (a) More Complex Solution BuyTickets Purchaser PaybyCredit > ChangeCancel > SelectTickets AddtoCart >

CS Test 2 Questions 1 (a) Incorrect Solution BuyTickets Purchaser PaybyCredit > ChangeCancel > SelectTickets AddtoCart

CS System Design: Data Intensive Systems Examples Electricity utility customer billing (e.g., NYSEG) Telephone call recording and billing (e.g., Verizon) Car rental reservations (e.g., Hertz) Stock market brokerage (e.g., Charles Schwab) E-commerce (e.g., Amazon.com) University grade registration (e.g., Cornell)

CS Example: Electricity Utility Billing Requirements analysis has identified several transaction types: Create account / close account Meter reading Payment received Other credits / debits Check cleared / check bounced Account query Correction of error etc., etc., etc., Architectural Style: Master File Update

CS Electricity Utility Billing First attempt: Data input Master file Transaction Bill Each transaction is handled as it arrives.

CS Criticisms of First Attempt Where is this first attempt weak? All activities are triggered by a transaction A bill is sent out for each transaction, even if there are several per day Bills are not sent out on a monthly cycle Awkward to answer customer queries No process for error checking and correction

CS Electricity Utility Billing Batch Processing: Edit and Validation Data input Master file Edit & validation read only errors Batches of validated transactions Batches of incoming transactions

CS UML Deployment Diagram: Validation MasterFile Check EditCheck ValidData DataInput RawData

CS Electricity Utility Billing Batch Processing: Master File Update Master file update Bills Validated transactions in batches Sort by account errors Reports Batches of input data Checkpoints and audit trail

CS Electricity Utility Billing Benefits of Batch Updating All transactions for an account are processed together at appropriate intervals Backup and recovery have fixed checkpoints Better management control of operations Efficient use of staff and hardware Error detection and correction is simplified

CS Architectural Style: Master File Update (basic) Master file update Data input and validation Mailing and reports Example: billing system for electric utility Advantages: Efficient way to process batches of transactions. Disadvantages: Information in master file is not updated immediately. No good way to answer customer inquiries. Sort

CS Online Inquiry: Use Case CustomerRep AnswerCustomer NewTransaction > A customer calls the utility and speaks to a customer service representative. The representative can read the master file, but not make changes to it. If the representative wishes to change information in the master file, a new transaction is created as input to the master file update system.

CS Online Inquiry Master file read only Customer Service Representative Customer Service department can read the master file, make annotations, and create transactions, but cannot change the master file. New transaction

CS Architectural Style: Master File Update (full) Example: billing system for electric utility Advantages: Efficient way to answer customer inquiries. Disadvantages: Information in master file is not updated immediately. Customer services Master file update Data input and validation Mailing and reports Sort

CS Data Intensive Systems with Real Time Transactions Transactions Received by mail or over telephone For immediate or later action Complex customer inquiries Highly competitive market Example: A Small-town Stockbroker

CS Real-time Transactions & Batch Processing Customer & account database Real-time transactions Data input This is a combination of the Repository style and the Master File Update style

CS Extending the Repository Architectural Style: A Small-town Stockbroker Databases Customer and account database Financial products (e.g., account types, pension plans, savings schemes) Links to external databases (e.g., stock markets, mutual funds, insurance companies)

CS Real-time Transactions Customer & account database Products & services database Real-time transactions External services

CS Real-time Transactions & Batch Processing Customer & account database Products & services database Real-time transactions Batch processing Data input External services

CS Stock Broker: Interface Diagram CustomerDB ProductDB OnLineTR BatchTR External

CS Practical considerations to include in Architecture and Specification Can real-time service during scheduled hours be combined with batch processing overnight? How will the system guarantee database consistency after any type of failure? reload from checkpoint + log detailed audit trail How will transaction errors be avoided and identified? How will transaction errors be corrected? How will staff dishonesty be controlled? These practical considerations may be major factors in the choice of architecture.

CS Systems Architecture for Network Systems: Firewall Public network Private network Firewall A firewall is a computer at the junction of two network segments that: Inspects every packet that attempts to cross the boundary Rejects any packet that does not satisfy certain criteria, e.g., an incoming request to open a TCP connection an unknown packet type Firewalls provide security at a loss of flexibility and a cost of system administration.

CS Time-Critical Systems A time-critical (real time) system is a software system whose correct functioning depends upon the results produced and the time at which they are produced. A soft real time system is degraded if the results are not produced within required time constraints e.g., a router is permitted to time out or lose a packet A hard real time system fails if the results are not produced within required time constraints e.g., a fly-by-wire control system for an airplane, must respond within specified time limits.

CS Time Critical System: Architectural Style - Daemon Daemon Example: Web server The daemon listens at port 80 When a message arrives it: spawns a processes to handle the message returns to listening at port 80 Spawned process A daemon is used when messages sometimes arrive at closer intervals than the the time to process them.

CS Software Considerations In some types of system architecture, non-functional requirements of the system may dictate the software design and development process.

CS Software Considerations: Time-Critical System Developers of advanced time-critical software spend almost all their effort developing the software environment: Monitoring and testing -- debuggers Crash restart -- component and system-wide Downloading and updating Hardware troubleshooting and reconfiguration etc., etc., etc.

CS Software Considerations: Testing Example: Testing multi-threaded and parallel systems Several similar threads operating concurrently: Re-entrant code -- separation of pure code from data for each thread May be real-time (e.g., telephone switch) or non-time critical The difficult of testing real-time, multi-threaded systems may determine the entire software architecture. Division into components, each with its own acceptance test.

CS Software Considerations: Continuous Operation Many systems must operate continuously Software update while operating Hardware monitoring and repair Alternative power supplies, networks, etc. Remote operation These functions must be designed into the fundamental architecture.