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Module 1: Modeling Techniques and Simulation

Apuntes
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In the lastclass we discussed about the graphical modeling techniques and we saw few techniquesfor data modeling. Basically, to identify the relationship between various entities in thesystem, how do you use the graphical modeling techniques to represent theserelationships? We saw a few diagrams like a entity relationship diagram or ER diagramwe saw about complex ER diagrams, and then we discussed about another diagramcalled higraph.So, all these used for basically modeling the data in the system or the relationshipbetween various entities in the system.(Refer Slide Time: 00:52)
Today we will discuss about the Process Modeling. As I explain the previous class aprocess model basically defines the functional decomposition of the system function andthe flow of inputs and outputs of a system. So, here it is more like the functionaldecomposition. So, we use the process modeling to identify the functions in the system,
how do we decompose the functions into small functions. So, that is the main purpose ofprocess modeling techniques.The one of the important diagrams use here is the known as the data flow diagram orDFD. In data flow diagram we try to identify. So, what processing is done, when is itdone, or how is it done and where by whom and for this what data is needed and bywhom for what and when. So, these are the things we need to represent using the dataflow diagram, basically looking at what process is done, when is it done, how is it done,or by whom it is done and what kind of data is needed and who provides the data, fromwhere the data comes, or where the data goes out and how the data processing is carriedout. So, these are the basic issues we represent using the data flow diagrams.Let us see how actually we can develop the data flow diagrams to represent theseprocesses and then see; what are the different ways of representing the data flowdiagrams. As we can see the basic constructs of DFD are function data flow, store andterminator. So, these are the 4 basic constructs for the data flow diagram, first one thefunction, as you know a function is the basic entity of any system. So, the function isbasically represent using a circle in the data flow diagram.(Refer Slide Time: 02:35)
So, we use 4 constructs. So, a circle or an oval is used to represent the function or thesystem. So, this is the first constructs and then we use another one called data flow. So,data flow is basically represented using arcs. So, we use this kind of arcs to represent the
data flow. We can actually have different kinds of arcs you can have a single arc or youcan have a branching arc, or you can have multiple branches also in the data flowdiagram. So, we can have multiple branches representing that the same data is being flowon to different entities.So, this is the function, this is the data flow, this is the construct one, this is the constructtwo data flow. The other one is known as a store or the storage space. So, this isrepresented in different ways you can represent the store. So, sometimes it is representedlike this as a store basically to store the data or to (Refer Time: 03:38) retrieve data fromthe store. So, we use the term store, or it is represented the sometimes like this also. So,this is the third construct used in data flow diagram. And the forth one is known as theterminator.So, terminator is nothing but a an external system represented using a square. So, this isthe terminator. The store represents the storage of data terminator represents thetermination of that particular process or the function where the output from the wholeprocess which go through the terminator and there the flow ends. So, these are the fourconstructs. So, we use a function or a system we represent using a circle or an oval.We use the data flow, we use arrows to represent the data flow, and then we have a storefor database and terminating the function or it more like an external system whichactually provides you, or it actually represents the end of that particular process. So, thatis the terminator. Let us take few examples to show how we actually represents or usethis kind of data flow diagrams to get the or to represent a particular process. So, let ustake a very simple example just to see a system taking data from the database andproviding to a customer. In the case of an ATM or in case of any other transaction withwe do the transaction if using a database, you can provide the data from the store andgive it to the customer.
(Refer Slide Time: 05:21)
So, here you can see that the system will be represented like this it is a very simplifiedrepresentation of a system. So, like it take an ATM as a system. So, this is a system andthen you will be having a database where the account holders will be kept. So, this is thestore or the database we called as database and from here the data will be going and therewill be a flow from here the information flow will be from this direction also and thenthis will go to the customer. So, here the customer will be the terminator, because thetransaction ends with the customer.So, customer will be the terminator here. So, this will be there and there will beinformation flow here. So, this is the very simple data flow diagram for a transaction. Ofcourse we need to represent all other transaction which is going on inside the ATM usingcomplex DFDs, but this is a very simple way of representing the transaction, you have adata base you have an ATM system and you have the customer.So, the data flows from the store to ATM storage or, database to ATM or request fordatabase is coming from ATM to database similarly the customer ask for sometransaction and ATM provides the transaction. So, it shows the processes or the flow ofdata within the system and it is components.As we can see here, we are using the system representation the storage representation aswell as the terminator and the data flows. So, that was a very simple example will take an
example of a credit card transaction and then see how to represent the transaction usingthe data flow diagram.(Refer Slide Time: 07:14)
So, here you can actually represent the customer as a terminator here, and then you willbe having different functions here.So, one is basically credit status that is the function. So, this is check credit status, that isone function, whenever the customer wants to have a transaction or when he places inorder customer makes an online order through credit cards, there will be a creditchecking by the system. So, if you can not the whole processing system as a if yourepresented it inside a box and you can see there are multiple functions one function is tobasically check the credit status.Then we will be having a data base which is basically the credit rating of the person; sothe data from the credit rating. So, there will be an enquiry from here to the credit ratingand then there will be another function which actually maintains the credit rating. So,maintain so this is another function maintain credit rating. So, based on this there will bea data flow from here and from to here.And based on this information, it receives the order will be validated. So, ordervalidation will be another function, this is the order validation and this will be connectedhere. So, validate the order is validated then this will be providing the service to the
customer. So, this again a flow, so here should I have one or we can have a reject orderbased on the validation. So, this can be a the order. So, we are placing an order here andthen this can be the rejection. So, based on the credit rating and they taking of the creditstatus, this will be rejected or accepted, it is accepted it will be validated here.So, it is validation of order. And finally, the goods will be delivered to the person. So,this is the data flow diagram, DFD for a credit card transaction. As we can see here arethe four constructs are here. So, this is the terminator which actually the process endswith the customer and as well as it starts with the customer, the customer places an orderan online transaction and there is a process or the function which actually check thecredit status of the person and to check that one relies on a database the credit ratingdatabase and based on that information the credit status it will be accepted or rejected,and it is accepted then it will be validated the order will be validated, that ordervalidation function will do that process and then once it is validated then they goods willbe delivers.And at the same time the credit rating will be updated based on the information providedto the database, and this maintenance of the credit rating will be done this process basedon the information it is gets from the credit rating database. So, this is the way how thedata flow diagram is created for a particular transaction. So, like this you can actuallyhave various transaction and various processes can be easily modelled using the dataflow diagram. Let us take one example for the system engineering design. So, as youknow that there are different processes in the system engineering.So, how do we actually represent the system engineering design process using a dataflow diagram? Since we are familiar with most of the processes involved in the systemengineering it will be easy for you to understand how that is represented using a dataflow diagram. So, here the user of course, it starts with the user.
(Refer Slide Time: 12:00)
And then there will be processes which actually surface the users. So, this is a process ofcustomer survey, or the uses survey to find out the requirements. And then this will beanalyzed by another process. So, there will be an analysis of the surveyor results,analysis and based on this will be having a preliminary design.So, based on the analysis will be having a preliminary design process. So, this is thepreliminary design. So, the I am just writing all the processes first, then we will look atthe database and the other transaction of the data. And once you have this preliminarydesign then there will be a strategy for the design of the hardware. So, there will be ahardware design or hardware study. So, study the possible hardware solutions, then wewill be going for the detailed design of the system.So, these are the main processes involved in the design, now you look at the what kind ofdatabase is needed for this kind of a design process. So, one is that there will be a designrepository or the design database. So, whenever you go for a preliminary design we lookat the existing designs. So, this is the design repository or were the we have differentdesigns already available. This is a design repository. So, there will be a interaction adataflow from here to here.So, whenever if you make a new design that will be going to the database if you want totake some existing design you will be taking it from the database and it will be using it.Similar, so this flow here is the user requirements, from the user then you have the
feasibility document, based on the survey and the analysis will be having a feasibilitydocument which is coming from the user survey and then again after analysis will betaking few more customize the requirement from the users. So, there will be anotherinput coming from directly to the analysis section instead of going through survey, theanalysis team will be directly interacting with the user to get more requirement or thespecific requirement of particular customers. So, that is the data flow from the user to theanalysis section and then there will be a another terminator which is known as a programmanagement it actually decides about the various strategies for the program or thedesign. So, this is the program management.So, it is again another entity which actually will be directly interacting with the analysisteam, giving the directions on how to proceed with the design. And then it will be havingthe hardware again based on the analysis will be having the hardware study, and thenthere will be other entities like hardware suppliers. So, there will be interacting with this,and then we will be having the final developer who actually produces the system.So, this is part of the design. So, the developer is the one who actually produces thesystem. So, we have detailed design that will be communicated to the developer willdesign the system and there will interact and design the system and deliver the system.So, these is the design depository the database and then second see here the interactionsare here design repository and the preliminary design, and this analysis one of the majorfunctions in the system design process. We can see there are lot of interaction with theother entities and you can see that flow of data in this particular process the survey datawill be coming the user requirements will be coming there similarly the programmanagement the requirement of the top level management in that particular design willbe coming.Similarly, the details of the hardware accessing hardware and the requirement ofhardware will be interacting with the analysis team. All these data is completed then itwill be going to the detail design of course, there will be an interaction between thedetailed design team and the analysis team also. So, here actually the systemspecification will be given system specifications, a system specs will be delivered to thedetailed design team. So, this shows the DFD for a design process. So, you can say this isthe data flow diagram for a design process.
So, by looking at this kind of data flow diagrams will be able to identify what kind ofinteractions are taking place between various processes or what are the main processesinvolved in the design and what kind of interactions are taking place, what kind ofdatabase is needed or what kind of data flow is taking place between different processescan be easily understood using the data flow diagram.(Refer Slide Time: 18:00)
That is one type of process modeling and another one known as N2 charts. So, N 2 chartsare basically or N 2 charts or sometimes it is known as a n square diagrams.(Refer Slide Time: 18:15)
So, the N square diagrams are basically a functional decomposition process it is givingalmost the same kind of information given by the IDEF0 diagram we discussed aboutIDEF0 diagram in one of the lectures earlier. So, why a similar kind of information isprovided by the N 2 diagrams. The name N 2 comes from the structure or the way it isappearing normally if you have N functions or N sub functions in a system.(Refer Slide Time: 18:49)
We write all those functions sub functions as a diagonal of a rectangular shape.So, we will write down all those functions as a diagonal of a rectangle. So, these are theN function. So, if you have N functions. So, it will make it as a N by N square, will makeit as an N by N array N represent the main functions along the diagonal. So, that is howthe name comes the N 2 diagram or N square diagram. Now the main functions will berepresenting along the diagonal and we give the number 1.0, 2.0, 3.0 and 4.0 and so on.So, this is the main function or the divided functions of a system now this functions arerepresented using a rectangle or a square shape and the other functions are written overhere, then the interaction between this functions are represented using something called Imean a shape like this. So, these are the rectangles represents the main functions or thefunctions will be represented here, these are the functions and the interactions arerepresented using we call it as the round tangles.
Basically a rectangle with the rounded corners. So, these actually represented theinteraction between different function. So, this is the interaction where you representedusing round tangles, and here the kind of data flow is represented using arrows here. So,if there is a data flow from this function to this function this represented like this and thisis the forward flow of data.Similarly, you can actually have this here also round tangles which actually representsthe interaction function or interaction between these functions. And whenever there is afeedback from this function to the other function then which will be given representedlike this here also again we will use the round tangles to represent the interaction.So, finally, you will be getting an N by N array, because when we have N functions alongthe diagonal you will be having an N by N array of functions as well as the interactionsand that is why this is known as an N 2 diagram or N square diagram by the convenientfor functional decomposition. As I mention it provides you almost the same data asIDEF0 diagram IDEF0 is more of a standard developed for the air force, but this iscommonly used diagram employed by many industries, is not a standardized one, but theactually provides you almost the same information as the IDEF0 diagram.You can use any one of these diagrams to represents the functional decomposition. So,this is the way how the interactions are represented, you can have many kind ofinteraction over here. And, you can have this actually directly interacting to this also likethat you can have all kinds of interaction can be easily represented using this N 2diagram can have the functions along the diagonal and the interactions represented alongthe sides. So, you can have on the right side will be more of a data flow to the nextfunction, on the left side will be the data flow back to the functions.Will take a few examples and then see how to use this kind of N 2 diagrams for actualfunctional decomposition. One familiar system should we have discussed few times isthe elevator system. So, we will see how to represent the functional decomposition ofelevator using the N 2 diagram. So, here as I mentioned we will start with sub functions.
(Refer Slide Time: 23:43)
So, we can actually identify many sub function for the elevator, the first one is the; I willwrite it as accept passenger request. So, this is one function.So, (Refer Time: 24:00) now 1 and then we have other functions. So, we have 1 2 3 4functions here. So, we will draw four rectangles. So, this is 2. So, accept passengerrequest then control elevator car, then move passengers basically move passengerbetween floors, then enable maintenance. So, these are the four main functions of theelevator. Now we need to find out what kind of interactions are taking place betweenthese functions and what kind of information processing confirmation is pass betweenthe functions.So, this can actually be represented using the N 2 diagram. So, we have 1 2 3 4 subfunctions, now you see what kind of inputs are. So, with this is the N 2 charts, basicallythis is the N by N array, now we can see what kind of inputs are coming to the functionexternal inputs can be represented and the top for are the sub functions. So, any inputcoming from the outside and that will curve here can be represented like this.For example this will be the request for service. So, that can be one inputs similarly youcan have different inputs like emergency support, or etcetera supports for those are theinputs coming to the first function accept passenger request similarly you will be havingthe input here as the elevator configuration, like this there maybe many inputs coming to
the system like regulations, safety regulations and the building regulations those thingsmaybe an input to the main net service.So, these are the input coming from the external to the system to this functions. Now youare to see what kind of inputs are coming from internally or from this functions. So, herethis will be the will be represented as using a round tangle. So, this is basically adigitized request. So, the digitized request will be coming from this function the firstfunction to the second function. So, this is the digitized request coming from here andthen flowing to this one. Similarly there will be a output coming from this function, thiswill be basically the assignment of cars.So, assignment of cars for various flows will be the output from here, which will begoing to the move passenger function. Similarly here sensed malfunction could be aoutput, so when there is a malfunction in one of the cars that will be sense and so thatwill be another output from here sensed malfunction. If any one of the car is notfunctioning, but that will be given as an input here and output and there will be given asan input to the enable maintenance.So, this way you can identify or the process or the information passing from one functionto other function. Similarly there will be a sensed malfunction coming from all thesefunctions. So, here if it is not working properly or there is a malfunction in one of thisfunction. So, this will be a sensed malfunction, similarly here also you can have a similarone. So, all these will be connected to this one. So, if there is any problem with any oneof these functions that will be sensed and that information will be passed to the enablemaintenance section.Similarly, there will be some kind of feedback coming here also, from move passengersthe output from here will be the present position of elevator, because we need thatinformation to provide the output to the passenger, or the feedback to the passenger. So,whenever there is a movement of passenger the position of the elevator will be given as afeedback. So, elevator position and direction of motion will be given as an output,through the complete elevator status will be generated here.So, elevator status and that will be going as a input to the accept passenger requestfunction. This is the output from here which is coming as a feedback to the first function.Similarly you can actually have this elevator maintenance also will be giving a output
here about the position of the status of elevator and that will be given as here and thencompare that output will be going to the accept passenger request function.It should be giving an output to the passenger. So, this is again a simplifiedrepresentation you can have more complex or you can represent all other functions alsoin this one. So, this is the N 2 diagram for elevator. So, this is almost similar to theIDEF0 diagram what you already studied you can see that these are the functions andagain you can actually go to the next level you can take this function alone and thenidentify all the sub functions and then again create another N 2 chart, and identify all thesub functions as well as the data flowing from one function the other function as well asthe feedback coming from the functions back to the sub functions.And here we can represent are the inputs to these functions. So, this can actually beextended you can have many charts like this and to find out all the sub functions as wellas to find out the interaction between these sub functions. Let us take one more example.So, here I am taking the example what we already discussed while explaining some ofthe system design examples. So, here I will take the example of the auto link system.(Refer Slide Time: 31:25)
So, we already discussed about the auto link system, which is a system developed forhelping the drivers to locate themselves and to get the directions as well as foremergency support.
So, in this auto link systems you want to develop a N 2 diagram, or the functionaldecomposition we will identify are the sub functions needed. So, we will write down thesub functions here like, perform client function then perform auto link function. So, theseare the sub functions. Perform emergency response function, then perform GPS function,GPS system function, we can consider these are the four main functions to be performedby the auto link system and then and it for request will be provided by this perform clientfunction and that will be passed to the auto link function.So, this request will be passed here and then there will be an emergency request functionbasically the auto link function one of the functions is basically to provide the emergencyservices. So, that emergency request will be passed to the emergency response function,and then perform the emergency response. So, here there will be perform emergencyresponse will be another function and similarly here from the GPS will be getting thedata GPS signals will be coming here.So, the GPS health status as well as the information, so the health status will be providedsorry the health status and there will be the GPS signals and this will be. So, this will beconnected to this one, this, this is GPS signals; here there will be the GPS data will becoming here and this information will connected to this one and this data will be comingof the health status and then the GPS signals will be coming and that will becommunicated to the auto link functions.So, this again a N 2 diagram or the functional decomposition using N 2 diagram for a anauto link system. So, like this you can actually develop the N 2 diagrams for manysystems or it can actually take some live examples of the system and the how variousorganizations work also can be represented using N 2 diagram. I will take a example canactually see it operational in various situations. So, this is basically a system were manyof the military or the spy agencies or organization which work different situations likeunderworld operations, or we need to have lot of secrecy in operations. So, suchorganizations try to have minimal communication between various entities.So, there may be having various organization entities and various organizationalfunctions, but they will try to ensure that the interactions between these entities are veryminimal. So, further they need to ensure that the transaction of data from one entity toother entities very minimal and there will not be any direct transaction of data or money
or whatever the other information is highly restricted. So, how these kind of organizationwork and how their functions can be represented using N 2 diagram. We will see anexample and then look at how they are successful in maintaining the secrecy of theiroperation by limiting the data exchange between various functional entities.(Refer Slide Time: 36:11)
So, I will take the something like a spy operation, spy or a undercover operations. So,though they are not really engineering systems, we can actually analyze their operationsusing the N 2 diagrams, I am trying to explain the utility of N 2 diagram under varioussituations. So, look at how they work basically there will be a function to manage theirrevenues.So, whatever maybe the operation there should be a entity which actually manages therevenues of the organization or the process, then there will be another function liesbasically the plan their operations, the other one will be distribution of funds,
then recruitand place operatives. So, they need to have people who can actually carry out their job.So, they need to recruit the people and then place the people are for different operations.Then they need to occur the necessary hardware, then the place the operatives so here itis recruit and train operatives basically.This is then the place the operatives and carry out task, and there maybe anotheradditional function also separate training function also can be added, but depending onwhether they recruit and training as a single function or recruitment is one particular
function and the training is another one, then there will be having a another functioncalled training or so. So, I am putting it as t r g training. So, these are the main functionswhich we can identify with any kind of operations, where they want to limit theinteraction between various entities.So, the person who is actually managing the revenue may not be knowing anything aboutwhat is happening over here because there may not be any interaction.