Workflows

Introduction

You decided to do a computational study. Great🔥! But what kind of study? The first distinction can be made between a data science project and simulation study. While having a similar skeleton (as we discussed before), there are essential differences such as setting up experiments, for example. There are other cool types of studies (i.e. network analysis, bio-statistics), but here we will focus only on those two.

Let's select a type of computational study for you

‌Each of these types has its sub-types or methods. Ideally, the chosen method should fit the problem and the purpose. If you think that the problem is can be better described in System Dynamics than Agent-based Modeling, then go for System Dynamics. It would pretty weird to model bathtub dynamics with myriads of agents, right🙃? Recall the law of the instrument and Abraham Maslow's quote:

"I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail."

Let's assume that you have a clue which type of study to select. Now it is time to dive deeper!

Data science workflows

TL;DR Use this.

Important to clarify the difference between data science and machine learning projects. Typically, the result of a data science project is an insight into a certain phenomenon. For example, we want to see what characteristics make people buy milk or what The Hague's neighbourhoods have in common. Such a study sometimes called exploratory data analysis (EDA). Machine learning (ML) projects are different. Consider a following example: you pass an image to the algorithm(-s) and want to know whether it is a dog or a cat. There is less uncertainty related to the problem of the study. The side tasks of ML projects are to find the best algorithm and hyperparameters. To progress in EDA you may think about collecting extra data, applying different types of algorithms.

As a result machine learning workflows are a bit different from data science ones. Here the focus is on the latest one.

Currently, there is no 🥇 standard of data science workflow. Let's introduce the ones that found useful and discuss their differences. Here is a list:

• CRISP-DM,

• OSEMN originally introduced by Mason & Wiggins and its slight modification AOSEMN by Clive,

• the approach suggested by Geron in his bestseller Hands-On Machine Learning with Scikit-Learn and TensorFlow,

• and finally data science process from the Harvard data science course described by Byrne (2017).

Apparently, they all have something in common😯. Let's compare them with old good table:

№	****CRISP-DM****	(A)OSEMN****	**[Geron (2017)*](https://www.amazon.com/Hands-Machine-Learning-Scikit-Learn-TensorFlow/dp/1491962291)\***	Byrne (2017).
1	Business understanding	(Abstract)	Frame the problem and look at the big picture	Ask an interesting question
2		Obtain	Get the data	Get the data
3		Scrub
4	Data understanding	Explore	Explore the data to gain insights	Explore the data
5	Data preparation		Prepare the data to better expose the underlying data patterns with ML algorithms
6			Explore many different models and short-list the best ones
7	Modeling	Models	Fine-tune your models and combine them into a great solution	Model the data
8	Evaluation	Interpret	Present your solution	Communicate and visualize the result
9	Deployment		Launch, monitor, and maintain your system

Let's examine the table from top to the bottom. First, OSEMN is missing an essential component, that the rest have: a problem or a question. Clive proposed to call it an abstract and put it on top of OSEMN. 🎩 and you have AOSEMN. Alright, to be fair, the abstract is more than that. It also somehow resembles so-called Readme Driven Development. Second, the bodies of the workflows seem pretty much similar. Only the bottom vary. CRISP-DM (stands for the cross-industry standard process for data mining, by the way😉) and Geron's approach have steps dedicated to deployment. It is unlikely that as a student you will have a need to do that. No, of course, it is important, but a research typically ends with an answer to a research question.

To go deeper into what exactly each of the steps require, click on the links and read. If you are a beginner 👨🎓 we recommend you to look at Geron's book. It has nice examples and pretty extensive explanations.

👨🏫 Advice: The workflows are pretty much the same 🎆 . By default use Harvard's one, but get familiar with the rest.

Simulation studies workflows

Alright! Instead of conducting a data science project, you decided to conduct a simulation study. Understandable! You want to test different policies on, let's say, a supply chain. The next step is to select an appropriate modeling paradigm. Typically, the main ones are:

What kind of simulation study fit the best?

Without a doubt, there are other important paradigms, but let's focus on these ones. Struggling with selecting? Take a look here at the work of Behdani (2012).

Kelton et al. (2011) proposed do differentiate the following steps in any simulation study:

1. Define high-level objectives and identify stakeholders.

2. Define the functional specification, including detailed goals, model boundaries, level of detail, modeling approach, and output measures. Design the final report.

3. Build a prototype. Update steps 1 and 2 as necessary.

4. Model or enhance a high-priority piece of the system. Document and verify it. Iterate.

5. Collect and incorporate model input data.

6. Verify and validate the model. Involve stakeholders.

7. Return to step 4 as necessary.

8. Design experiments. Make production runs. Involve stakeholders. Return to step 4 as necessary. Document the results and the model.

9. Present the results and collect your kudos.

Agent-based modeling

Agent-based modeling (ABM) is a systems modeling worldview in which a problem is decomposed into individual entities (or "agents"), their relevant (inter)actions, and the environment in which they act. An example might be a population of wolves and sheep on a grassy field. The emphasis is on space, and relations and interactions between individuals.

System dynamics

Overview of the SD modeling approach according to Richardson & Pugh (1981)

System Dynamics (SD) is a systems modeling worldview in which a problem is decomposed into "stocks" (accumulations of things, such as liters of water in a bathtub, Euros in a GDP, or patients in a healthcare system) and "flows" (change rates of those accumulations, such as liters per minute, circulated Euros per month, new patients per day). The emphasis is on high-level effects such as feedbacks and delays.

Discrete-event simulation

Discrete-event simulations (DES or DEVS) is a systems modeling worldview in which a problem is decomposed into interacting processes. It bears many similarities to ABM, but the emphasis is the processes, rather than the entities being processed. An example might be a factory floor, where entities are delivered at one end, and then go through a number of manufacturing steps before leaving the factory at the other end.

References

1. Behdani B. Evaluation of paradigms for modeling supply chains as complex socio-technical systems. InProceedings of the 2012 Winter Simulation Conference (WSC) 2012 Dec 9 (pp. 1-15). IEEE.

2. Richardson GP, Pugh III AI. Introduction to system dynamics modeling with DYNAMO. Productivity Press Inc.; 1981 Jan 1.

3. Kelton, W. D., J. S. Smith, and D. T. Sturrock. 2011. Simio and Simulation: Modeling, Analysis, Applications. 2nd ed. New York: McGraw-Hill, Inc (p. 17).