III. Structured Analysis and Design Technique (SADT) SADT: Structured Analysis and Design Technique

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1 III. Structured Analysis and Design Technique (SADT) Hisry Data and Activities SADT Diagrams The SADT Analysis Process Data Flow Diagrams 2004 John Mylopoulos SADT -- 1 SADT: Structured Analysis and Design Technique Diagrammatic notation for constructing a sketch for an application. Offers boxes represent entities and activities. Offers a variety arrows relate boxes. Boxes and arrows have an associated (informal) semantics; users are aided by box and arrow labels, other informal documentation. Has inspired many other commercial ols. Has been in use since the mid-seventies [Ross77]. SADT is available as a commercial CASE ol under the name IDEF John Mylopoulos SADT -- 2

2 SADT Notation Control Inputs. Label Outputs Needs & Desires Market Experience An SADT diagram consists boxes and arrows Food&Clothing Money RunHousehold Payments Plan&Budget 2004 John Mylopoulos SADT -- 3 SADT Primitives Things and happenings Things -- objects, data, nouns, information, substances, passive Happenings -- operations, activities, verbs, processing, events, active Two types boxes: data boxes, activity boxes Boxes interconnected through arrows, form a diagram. Each diagram includes up six boxes; each box has its own diagram, leading hierarchical models activities and data John Mylopoulos SADT -- 4

3 An SADT Activity Seed & Vegie Prices Plan & Budget Weather Budget Plan Money Buy Supplies Fertilizer Seeds Cultivate Plants Pick Produce Extract Seeds Grow 2004 John Mylopoulos SADT -- 5 Semantics Arrows For activities Inputs are data that are consumed by the activity Outputs are produced by the activity Controls influence the execution an activity but are not consumed For data Inputs are activities that produce the data Outputs consume the data Controls influence the internal state the data 2004 John Mylopoulos SADT -- 6

4 Seed &Vege Prices A Parent Activity Prices Weather Purchased Goods Food Run Household Plan & Budget Market Experience Payments Satisfaction Farm Supplies Grow Sell Money Money Run Farm 2004 John Mylopoulos SADT -- 7 A Data Diagram Follow Plans Cultivate Respond Weather Select Allocate Buy Seeds Satisfaction Plant Plants Observe Harvest Produce Sell Eat Extract Crops 2004 John Mylopoulos SADT -- 8

5 The SADT Process Diagrams are created in a p-down fashion: a box in one diagram becomes a diagram in its own right with its own internal structure. Diagram decomposition is the main vehicle for refinement. However, this does not necessarily correspond aggregation in conceptual modeling. For example, the boxes inside a box may represent specializations the concept represented by the box, or even instances John Mylopoulos SADT -- 9 Technical Operational Economic Assessment Assessment Assessment What Model Technical assess- ment is concerned with system architecture. Operational assess- ment is concerned with system performance. Economic assess- ment is concerned with cost and impact system implementation and use. Context Analysis Functional Specification Design Constraints Current Operations Proposed Functions Resource Specs Problem Statement Perfrmance Parameters Usage Conditions Sensitivity Facrs Expected Impacts Expected Costs 2004 John Mylopoulos SADT -- 10

6 Roles in the SADT Process Authors - the developers an SADT model. Commenters - review the work authors. Readers - the eventual users the SADT diagrams. Experts - persons from whom authors obtain specialized information about requirements and constraints. Technical committee - technical personnel responsible for reviewing the SADT model at every level. Project librarian - responsible for all project documents. Project manager - has overall technical responsibility for the system analysis and design. Monir (Chief analyst) - an expert in SADT who assists and advises project personnel in the use SADT. Instrucr - trains authors and commenters on SADT John Mylopoulos SADT The Data Flow Model The Data Flow Model models flow information within an organization Source or destination information (internal or external entity) label Flow information Process which trasforms information Information sre Note: An external entity is explicitly outside the system boundary, while an internal one is inside John Mylopoulos SADT -- 12

7 instrucr(1) lecture notes, course refs assignment Read asst open questions Doing An Assignment instrucr(2) Update reference material Use library lecture notes, course refs lecture notes, course refs possible solution questions assignment handed in library sre Work on problem solution Write solution 2004 John Mylopoulos SADT The Computer Books By Mail Corp. The CBM (Computer Books by Mail) Corporation was recently acquired by a national holding corporation and is now a division. Established 12 years ago, the company's business has been act as book-jobber, receiving from librarians for books about computers, ing the books from the appropriate, at a discount, and filling the on receipt the books from the. Invoices are produced by a service bureau computer from forms filled out by CBM staff. Business is currently running at about 100 per day, each with an average 4 book titles and an average value per $150. The new management plans expand the operation considerably, improving service levels by holding scks the 100 most frequently ed book titles and making it possible for all pressionals (not only librarians) by calling a ll-free number, (800-DP-BOOKS, course) as well as by mail, as at present. This will create problems credit checking and create the need for an invenry control system some sort. The people who take the over the phone will need rapid access a catalog books verify authors and titles and be able advise callers what books are available on any given pic John Mylopoulos SADT -- 14

8 The Computer Books By Mail Corp. The volume transactions on the new system will, course, depend on the acceptance this new method ing, but it is projected grow 1,000 per day or more, though with a lower average books per (since librarians tend more books at a time than pressionals). A systems analyst has been assigned this newly acquired division with the responsibility investigating and specifying the new system on behalf the Vice President Marketing. Alternative Scopes Computerize the verification process. Computerize accounts receivable. Integrate verification, requisitions and accounts receivable. Of course, each one these alternatives will have different budget and project-length implications John Mylopoulos SADT The Computer Books By Mail Corp. Step I: Draw a Context DFD... describe the proposed system's relationship the rest the world System Cusmer (with books) Process credit status Cusmer Data Cusmers books and get back Processing fetches information from a book information sre ( the book, price,...) and from a cusmer information sre (is cusmer's account current?) 2004 John Mylopoulos SADT -- 16

9 Step II: Draw Level 0 Diagram -- Show interfaces between organizational boundaries Data book Cusmer is requisition cusmer credit status Pending Orders Cusmer Data Processing involves checking the and assembling a requisition the John Mylopoulos SADT Step II (cont'd): Further Expansion Data book Cusmer is cusmer credit status batched date PO# Pending Orders requisition (with books) cusmer Cusmer Data for title Assign Shipment titles quantities Orders correct s consignment note 2004 John Mylopoulos SADT -- 18

10 Step III: Refine Model Show Work Performed Within a Single Organizational Unit Explosion a process in another DFD Do level 1, 2, diagrams until you have enough Step IV: Show detailed processing within each transaction s Extract for a ing info unit date, PO # Retrieve ing info Compute copies for each book Note info in, terms business requisition tals by title (PO) Create PO copy Create PO in-progress record PO 2004 John Mylopoulos Pending Orders SADT Conceptual Modelling Data CSC2507 book The Computer Books By Mail Corporation Cusmer (with books) cusmer Apply Payment note copy A/C receivable is cusmer credit status Cusmer Data Create copy for title Pending Orders Assign Shipment titles quantities requisition Orders correct s consignment note Prepare vendor 2004 John Mylopoulos SADT batched A/C payable accounts due cheques s accuracy

11 Data Alternative I Computerize verification process Cusmer (with books) cusmer Apply Payment note copy A/C receivable book is cusmer credit status Cusmer Data Create copy for title Pending Orders Assign Shipment titles quantities requisition Orders correct s consignment note Prepare vendor 2004 John Mylopoulos SADT batched A/C payable accounts due cheques s accuracy Data Alternative II Computerize accounts receivable Cusmer (with books) cusmer Apply Payment note copy A/C receivable book is cusmer credit status Cusmer Data Pending Orders Assign Shipment 2004 John Mylopoulos SADT Create copy for title batched titles quantities requisition Orders correct A/C payable Prepare vendor accounts due accuracy s consignment note cheques s

12 Data Alternative III Integrate verification, requisitions and accounts receivable Cusmer (with books) cusmer Apply Payment note copy A/C receivable book Assign Shipment A/C payable accounts due accuracy Prepare vendor 2004 John Mylopoulos SADT is cusmer credit status Cusmer Data Create copy for title batched Pending Orders titles quantities requisition Orders correct s consignment note cheques s What Does This DFD Say? Donor Donation Info Record Donation Donation Form Donation Form New Donations New Donations New Donors Donors List New Donations Rare Donors Invenry Screen Donation Update Central Databases Handle Rare Bloor Request Process Request Donor Information Donor List Copy Rare Reply Donor Info Request for Donation Rare Request Delivery Request Hospital 2004 John Mylopoulos Donor Hospital SADT -- 24

13 References [DeMarco78] DeMarco, T., Structured Analysis and Systems Specififcation, Prentice Hall, [Gane79] Gane, C. and Sarson, T., Structured Systems Analysis, Prentice Hall, [Ross77] Ross, D. and Schoman, K., "Structured Analysis for Requirements Definition", IEEE Transactions on Stware Engineering 3(1), January [Yourdon89] Yourdpn, E., Modern Structured Analysis, Yourdan Press, [Ross77] Ross, D., Structured Analysis: A Language for Communicating Ideas, IEEE Transactions on Stware Engineering 3(1), Special Issue on Requirements Analysis, January 1977, [Ross77a] Ross, D., and Schoman, K., Structured Analysis for Requirements Definition, IEEE Transactions on Stware Engineering 3(1), Special Issue on Requirements Analysis, January 1977, [Wirth71] Wirth, N., Program Development by Stepwise Refinement, Communications the ACM 14(4), , John Mylopoulos SADT -- 25