What are Workflows?
Before we can discuss how Maestro can help you, we must first cover the most basic question: what are workflows? There are many definitions of workflow, so we try to keep it simple and define the term as follows:
You may not realized it, but you are surrounded by workflows! Everything from daily activities to recipes to the commands you run in a terminal can be broken down into a set of focused steps that have dependencies on one another. For example, you can't make bread without first mixing in the dough, then letting it rest, and then mixing in the yeast. Similarly, if you're running computational simulations, your workflow might look like: set up simulation inputs, then simulate, then post process results. Both of these lists are describing processes as a set of intent-driven steps and say nothing about implementation. As our analogy exposes, there are different perspectives of workflow as follows:
- Intent: The high level objective(s) that a step is defined to accomplish at a human understandable level, removed from details such as code and tools
- Implementation: The technical details such as tool or code choice, and other specifics about how to technically execute a step
An Example of Intent and Implementation
Let's start with the recipe for baking. The steps for baking bread are roughly as follows:
- Mix flour and water
- Mix in the yeast
- Fold the dough
- Proof the dough
Now, these steps are the procedural intent of achieving bread, not the implementation for how to create bread. For example, achieving a mixture of flour and water can be done in a few ways:
- Manual mixing with your hands in a bowl
- Mixing the flour and water with a whisk
- Using a standing mixer with a dough hook
All of these are implementations of how to achieving mixing flour and water. Software workflows behave the same way. For example, maybe you need to run a particle simulation. The first thing that needs to be communicated is the intent to run such a simulation (perhaps of some phenomena to be studied). Now, once the intent is established, you may need a particular simulator or tools -- all of which fall under implementation just as you would have a choice to achieve mixing by hand, whisk, or mixer.
Both intent and implementation are important perspectives to view workflows; however, one or the other is more important depending on context. Often times, intent and implementation are conflated which makes communication of a workflow process muddied at best. When you are communicating workflows, intent takes center stage. Intent is everything about why something is being run and describes the motivation for executing a workflow. Maestro aims to help researchers communicate intent by arming them with the vocabulary to do so while also providing the ability to easily automate their work at the same time.
Why are Workflows Important?
Software workflows are the backbone of computational science -- they are the means by which computational work is communicated, shared, and executed. For most users of HPC resources, the natural choice is shell scripting. These workflows usually vary in complexity, ranging from small sets of runs to large sets of runs (also called "ensembles") and are submitted to a batch-scheduled cluster. These scripts commonly are heavily coupled to a user's environment, contain hardcoded elements, and in most cases only work on the platforms they are written for. Similar to all other code, the typical workflow is a documented record of explicit commands to implement a process in the same way lines of code are explicit in their meaning; in both cases the statements themselves do not communicate why they were written. Documentation and commented code are how software developers and engineers communicate intent behind the explicit implementations of code.
A Technical Example of Intent vs. Implementation
Let's take a look at a function that simply squares an integer. Based on the function definition below, we can see that the function intends to compute the square of the integer
Without any implementation at all, the definition and comment (specifically docstring) communicates what the
square_number function achieves. This achieves:
- Someone who encounters this function in a library or in code can read a human-readable description about what the function achieves.
- Because the intent of the function is documented, and therefore understood, it can be debugged more easily.
- When communicating with another developer or engineer, one can simply use the language "square the number" which can then be mapped to implementation via the function.
Related, similar concepts appear in defining workflows.