Pipelines

A pipeline is a series of data-processing steps in RiskScape. RiskScape uses pipelines to transform rows of data, or tuples, as they flow through the system.

All RiskScape models are implemented using an underlying pipeline. However, advanced users can define their own models directly in pipeline code. This lets you interact with RiskScape’s data-processing at a much lower level.

Tip

For a how-to guide to writing pipelines see How to write basic pipelines.

Steps

A pipeline is made up of one or more steps. A step is a component that will process tuples. For example, the input step will output tuples from a data source, whilst the filter step will remove tuples that do not match the filter expression.

Steps get chained together, so that the output from one step feeds into the input for another step.

Most steps have parameters that are used to alter how the step processes tuples.

RiskScape has many built-in pipeline steps. The steps available, and their associated parameters, can be seen here

• Pipeline steps
  • input
  • filter
  • join
  • unnest
  • select
  • sort
  • group
  • save
  • enlarge
  • union

This help can also be accessed within RiskScape, using the following commands:

riskscape pipeline step list
riskscape pipeline step info STEP_NAME

Defining pipelines

Pipelines can be defined in the project file as a pipeline model.

The following sections use a simple pipeline example that:

• takes some assets

• filters them to remove assets that are not constructed from timber

• joins the assets to their region

We will explain how the definition works in the following sections.

Pipeline file

The pipeline can be defined in a separate text file, e.g. my_pipeline.txt:

input('regions.shp', name: 'region') as regions
input('assets.csv', name: 'asset') -> filter(filter: asset.construction = 'timber')
join(on: region.name = asset.region) as with_region
filter -> with_region.lhs
regions -> with_region.rhs

Then a pipeline model entry is added to the project INI file with a location pointing to that file.

[model my_pipeline]
framework = pipeline
description = demonstrates how to write a pipeline

location = my_pipeline.txt

In project INI

Pipeline models can also be defined in the project INI file itself with a pipeline entry. For example:

[model my_pipeline]
framework = pipeline
description = demonstrates how to write a pipeline

pipeline = \
  input('regions.shp', name: 'region') as regions \
  input('assets.csv', name: 'asset') -> filter(filter: asset.construction = 'timber') \
  join(on: region.name = asset.region) as with_region \
  filter -> with_region.lhs \
  regions -> with_region.rhs

Note

Pipelines defined in an INI file need an \ at the end of every line, except for the last line. This is because the INI file format expects entries to only span one line. The \ is a line continuation that makes the following line part of the current entry.

Defining steps

Steps are defined in a similar syntax to functions:

step_id([optional parameter, ...])[as optional_name]

The step_id specifies the type of step to use. It must correspond to one of the IDs listed in riskscape pipeline step list. The optional_name is used to uniquely identify the step in the pipeline.

Some examples of defining the same pipeline step:

input('my_bookmark')

With a step name:

input('my_bookmark') as input_assets

With parameter keywords:

input(relation: 'my_bookmark')

If you do not specify a step name, RiskScape will assign a default identifier to each step. The default name is simply the step_id, e.g. input. To ensure the name is unique, RiskScape may also append a number that reflects the order the step appeared in the pipeline, e.g. input_2, input_3, etc.

Tip

You only need to assign a step name if you want to reference your step from elsewhere in the pipeline. For example, a join step requires two inputs, so at least one of them will be a reference to another step.

Connecting steps

Steps are connected together so that the output of one step is passed to the input of the next. When multiple steps are connected together, they are called a pipeline chain.

Connecting steps is done with the -> operator. For example:

source -> destination

The source and destination in this example must both be unique pipeline steps, but they can be either:

• a step definition e.g. input() as my_input

• the name of a previously defined step e.g. my_input

The exception to this is where the destination step has more than one input, such as a join. In that case the destination must be <step-name>.<input-name>. Input names are listed in the riskscape pipeline step list output for steps that require them.

There are examples of both of these in the Defining Pipelines example above.

Tip

When you reference a previously defined step, make sure you have explicitly named the step. RiskScape will implicitly assign a unique name to each unnamed step, e.g. select({*}) might be named select_2. However, these implicit names can change as you edit your pipeline, so it is not recommended to reference an implicit step name.

Advanced pipeline features

This has covered the basics of defining pipelines. You may be interested in more advanced topics, such as Customizing your own model parameters.