Project layout

The PDM project contains two top-level packages, ska_oso_pdm.entities and ska_oso_pdm.schemas as shown in the figure below. The ska_oso_pdm.entities package contains Python object models for the logical entities in the SB data model. The ska_oso_pdm.schemas package contains code to transform the classes defined in ska_oso_pdm.entities to and from JSON.


Project layout and naming conventions.

The project layout and naming conventions are:

  • The SB data model is divided into logical groups that collect related entities together.
  • For each SB entity grouping, a corresponding Python module is created in ska_oso_pdm.entities and ska_oso_pdm.schemas. If the grouping is complex and contains many entities, the modules may be located inside a dedicated package for the group.
  • Python classes representing the SB data model entities are found in the corresponding ska_oso_pdm.entities module/package.
  • Marshmallow schema to transform ska_oso_pdm.entities objects to and from JSON are found in ska_oso_pdm.schemas.

Entities overview


Overview of PDM entities

The Python object model for the entities defined in the SB data model are located in the ska_oso_pdm.entities package. In general, each SB entity is represented as a Python class and each entity attribute presented as a class attribute or property.

PDM attributes can be typed as plain Python data types (strings, floats, etc.) or, where appropriate, represented by rich objects if this provides additional value to the client. For example, while astronomical coordinates are represented by floats and strings in the JSON schema, in the object model they are defined as Astropy SkyCoord instances to ensure ensure correct coordinate handling and permit easier manipulation downstream. Similarly, quantities with units could be defined as instances of Astropy Quantity to provide additional functionality.

For details on the entities modelled by this library, see the pages within the API documentation.

Schemas overview

Classes to marshall the ska_oso_pdm.messages objects to and from JSON are defined in the ska_oso_pdm.schemas package. This project uses Marshmallow for JSON serialisation. Classes in the ska_oso_pdm.schemas define Marshmallow schemas which are used by Marshmallow during JSON conversion.


Schema mapping for ska_oso_pdm.entities package


Schema mapping for ska_oso_pdm.entities.sdp package