# Glossary¶

DAG

DAG stands for directed acyclic graph, and it’s the most widely used data structure for data worflows:

• It’s a graph (in the mathematical sense) since it connects a set of steps (in the case of Orchest, a Pipeline step).

• It’s directed because those connections have a specific direction (from one step to the other). For example, a step loads the data, and hands it to the following step to process it.

• It’s acyclic because it has no cycles (or feedback loops). In other words, there is no way to follow the connections of the graph starting from one step and come back to the same step. This is important because it means that the execution of a pipeline is guaranteed to finish at some point.

Pipeline step

A single unit of execution, that receives data, operates on it, and outputs it (which can be retrieved by a next step).

• Has a one-to-one relationship with an executable file, which runs inside its own execution Environment, powered through containerization. This executable file can be edited through Orchest’s JupyterLab integration.

• Is executed as part of a Pipeline run.

• Has an execution state, i.e. READY, PENDING, RUNNING, COMPUTED, ABORTED or FAILURE.

• A step can have a set of parameters, all of which have to be given a default value. (The set of parameters can also be empty, thus the step not having any parameters.) These parameters are stored inside the Pipeline definition and are accessible inside the execution environment.

(Data science) pipeline

A DAG of pipeline steps defined in its respective Pipeline definition.

Pipeline definition

A file with the .orchest extension inside the project directory. The pipeline editor you see in Orchest is a UI handle to the file containing the pipeline definition.

• The JSON inside the file uniquely defines the pipeline.

• Every pipeline definition in a project is automatically detected and listed in the Orchest UI under Pipelines.

• A full JSON Schema definition can be found in the .

Interactive session

Some notion of a session that you can boot and shut down which gives you additional functionality when it comes to editing and running your pipelines. The lifetime of a session can be managed inside the pipeline editor. A session is automatically started for you when opening up a pipeline.

Pipeline run

Abstraction to execute pipelines.

• Can be scheduled to run at a specific time (through jobs).

• If parameterized, runs for selected (by the user) default values. If not parameterized, runs without any parameter values.

Interactive (pipeline) run

A pipeline run that runs instantly and that actively changes the pipeline directory’s filesystem. These interactive pipeline runs can only be run during an Interactive session inside the pipeline editor.

Non-interactive (pipeline) run

A pipeline run that runs on its own snapshot of the pipeline directory. This type of pipeline run is the building block of jobs.

Job

A set of pipeline runs (where each pipeline will run for a different set of parameters). Currently we support the following types of jobs:

• Grid search like jobs: a collection of non-interactive pipeline runs that is scheduled to run at a later time. The user can specify values for the parameters other than the default values. The scikit-learn docs are a great resource to read more about grid searches.

• Cron jobs: similar to grid search like jobs, but running on a cron schedule.

Read the section of the documentation to know more.

Environment

The runtime environment of a pipeline step. Using environments you can install additional packages and make changes to the base image directly.

Edit mode

Edit, create and run your pipelines inside the pipeline editor.

View your pipeline and its results from a past run (mainly applicable in jobs).

• A pipeline from read-only mode can be created into a pipeline in edit mode. This can be useful if you want to actively play with the environment that produced the results (state is not stored after execution has finished, unless it is an interactive run).