Information Systems Development MIS331 Logical and Logic Modeling 1/17/2019 MIS331

Agenda System Modeling Logical versus Physical Process Modeling with Data Flow Diagrams Logic Modeling 1/17/2019 MIS331

Process Modeling Graphic representation of functions or processes which capture, manipulate, store, and distribute data. System boundary is defined by where the data enters and exits the system Takes advantage of the concept of functional decomposition Process models can be constructed in a layered fashion such that increasing levels of complexity can be illustrated 1/17/2019 MIS331

Data Flow Diagram (DFD) Identifier Process Name Gane & Sarson Nomenclature Process Data Store File Name Entity Name Source/Sink Data Flow 1/17/2019 MIS331

Process versus Entity How do we decide if something is a process or an entity? If this “something” alters data as a function of the system then it is a process. creates a report, sorts, calculates, reads or writes, etc. If this “something” simply generates data as input to the system or accepts data as output from the system then it is an entity. customer submits an order customer receives item ordered Processes are inside the system boundary, entities are outside 1/17/2019 MIS331

Coding the Process Identifier Context level defines the entire system and its external entities Level 0 defines the primary individual processes identifier is X.0 where X equals the process number Level 1 first decomposition of Level 0 processes into sub-processes identifier is X.Y.0 where Y equals sub-process number Level n the result of n nested decompositions identifier is X.Y. ... .n.0 Functional Primitive Level lowest logical level where no further decomposition yields benefits 1/17/2019 MIS331

Simple System Decomposition 1/17/2019 MIS331

All data flows must begin and/or The Rules of DFDs In a nutshell… All data flows must begin and/or end at a process, because data flows either initiate or result from a process. 1/17/2019 MIS331

Three Basic Illegal Data Flows Entity Name Identifier Process Black Hole Identifier Process Name File Miracle 1.0 Create Paychecks Employee File Gray Hole 1/17/2019 MIS331

Logic Modeling Logic Modeling is logical but it is not Logical Modeling Logical Modeling is the representation of processes and their relationships to other processes. Logic Modeling is the representation of the internal structure and functionality of processes and subprocesses. How are inputs converted to output? When does a process occur? When should a process not occur? 1/17/2019 MIS331

Logic Modeling Tools Structured English Decision tables and trees just a modified version of good ol’ English Decision tables and trees models of conditions and actions as tables or graphs State-transition diagrams and tables shows the various states a system component can assume events that result in a transition from one state to another 1/17/2019 MIS331

Structured English Take the hours_wrkd and multiply them by Relies on strong, imperative verbs and noun phrases read, write, sort, move, add, begin, end, etc. uses only nouns and terms previously defined in the data dictionary Undefined adjectives or adverbs are not used unless clearly defined in the data dictionary as value ranges for data element descriptions avoids the construction of compound sentences Take the hours_wrkd and multiply them by the pay_rate and then put this value into the field called gross_pay. Calculate gross_pay using the formula: hours_wrkd * pay_rate. 1/17/2019 MIS331

Decision Tables Better than Structured English when logic becomes nested and complex If Employee=“S” then pay base salary else, If Employee=“H” then calculate wage and If hours_wrkd < 40 then produce absence report else, If hours_wrkd are > 40 then calculate overtime. 1/17/2019 MIS331

Decision Tree Depicts the decision scenarios as a connected series of nodes and branches which ultimately end in one or more actions probabilistic and nonprobabilistic probabilistic trees allow for condition probabilities to be carried throughout the decision process Nodes are decision points Branches are alternative paths Actions are the expected result of a decision based on the variables or constraints in place 1/17/2019 MIS331

Decision Tree If Employee=“S” then pay base salary else, If Employee=“H” then calculate wage and If hours_wrkd < 40 then produce absence report else, If hours_wrkd are > 40 then calculate overtime. Salaried? Pay base salary 1 Pay hourly wage Absence report < 40 = 40 2 Pay hourly wage Hourly? > 40 Pay hourly wage Pay overtime wage 1/17/2019 MIS331

When to Use What 1/17/2019 MIS331

For Next Time More on DFDs on Thursday Get a good grip on this material It may show up on a knowledge demonstration Case #1 Presentation on Tuesday Get prepared for Group A’s presentation Know Case #1 inside and out. Start thinking about KD #1 It will be here before you know it… 1/17/2019 MIS331