Fundamental SKA Software Standards

These standards underpin all SKA software development. The canonical copy of this information is held in eB , but the essential information is on this page, which is extracted from the eB document.





Architectural Decision Record




Application Programming Interface


Berkeley System Distribution


Central Signal Processor


Originally “Compute Unified Device Architecture”, now an Nvidia trade mark




Field Programmable Gate Array


Hardware Description Language


International Electro-technical Commission


Institute of Electrical and Electronics Engineers


Internet Engineering Task Force


Integration and Test Facility


International Standards Organisation


Large Synoptic Survey Telescope


Large Synoptic Survey Telescope Data Management element


Low Frequency Aperture Array


Local Monitoring and Control


Non Image Processing


Re-Structured Text


Request for Comment


Science Data Processor


Square Kilometre Array


SKA Organisation (before 1 May 2021) or SKA Observatory (after 1 May 2021)


Very High Speed Integrated Circuit (VHSIC) Hardware Description Language


Explanation of terms

In this document, terms in bold italic font are terms that have a specific meaning in the document. The first usage of the term will generally represent a definition. For example, in this document:

  • A Hardware Description Language is a specialized computer language used to describe the structure and behavior of electronic circuits, and most commonly, digital logic circuits 1.

  • Firmware is a combination of a hardware device and computer instructions or computer data that reside as read-only software on the hardware device 2.

  • Software includes the software portion of firmware as well as traditional software, in both source code and binary code form. In this document software also includes source code and binary Hardware Description Language artefacts associated with programmable electronic circuit design. This will be referred to as FPGA software.

  • SKA Software is software that is essential for the SKA Observatory to be supported and operated.

The inclusion of firmware into the software definition follows ISO/IEEE conventions. The inclusion of Hardware Description Language code development (i.e. FPGA software) into the software definition is unusual, and only applies in this document. Occasionally the word software is used in its ISO/IEEE sense (i.e. not including HDL code development) and in these cases it is not written in bold italic font. It is accepted that the use of Hardware Description Language in the title of this document is not required according to the definitions above, but it was included in the title for clarity purposes.

Purpose of the document

This document outlines standards that are applicable to all SKA software.

Scope of the document

The scope of these standards includes all SKA software and the infrastructure associated with it.

SKA software lies on a spectrum comprising:

  1. Off-the-shelf software, which is software that was not written specifically for the SKAO. This includes, for example:

    1. Operating systems

    2. Compilers

    3. Database software

    4. Desktop applications

    5. FPGA development tools and IP cores.

  2. Derived software, which is software that has some modules written or modified explicitly for the SKAO, but which also includes some modules that were originally developed for some other purpose. Examples include:

    1. Framework software such as the Tango control system.

    2. Business software such as procurement software which may be heavily customized for the SKAO.

    3. Software that has been written for a similar purpose for another telescope and has been adapted for use for the SKA Observatory.

  3. Bespoke software is software that has been written specifically for the SKAO. This includes, for example:

    1. Control and monitoring software such as Tango device servers.

    2. Data-driven data processing software for SDP and the Non-Imaging processing software.

    3. Web based software with database backends for observation and user management.

    4. Much of the FPGA software for SKA-Low and CSP.

Derived software is a continuum that ranges all the way between pure off-the-shelf software and pure bespoke software. And the standards that are applicable are also a mixture of the standards for the two extremes.

In the following, there are explicit standards that apply to off-the-shelf software and bespoke software. In general, the former will apply to the non-SKA (i.e. the off-the shelf) modules of derived software, and the latter to SKA specific (i.e. the bespoke) modules. Developers should make every effort to clearly distinguish between the two types of modules within a derived software system so, for example, it is possible to automatically separate the two for metrics evaluation.

However, the area is complicated (for example, some open-source off-the-shelf components may satisfy most of the bespoke software requirements) and so these standards must be applied intelligently as guidelines for derived software. In most cases a common-sense approach can be taken.


Applicable documents

The following documents are applicable to the extent stated herein. In the event of conflict between the contents of the applicable documents and this document, the applicable documents shall take precedence.

  1. SKA-GOV-0000086 SKA Observatory Intellectual Property Policy

Reference documents

The following documents are referenced in this document. In the event of conflict between the contents of the referenced documents and this document, this document shall take precedence.

  1. ISO/IEC 12207:2013 Systems and software engineering – Software life cycle processes.

  2. Clement et al, Documenting Software Architectures: Views and Beyond, Second Edition Addison-Wesley, 2011.

  3. ISO/IEC/IEEE 42010:2011(E), Systems and software engineering — Architecture description 2012.

  4. IEC 62682:2014 Management of alarms systems for the process industries.

  5. Semantic Versioning 2.0.0.

  6. The SKA Developer Portal.


  8. SKA-TEL-SKO-0001065 Solution Intent Definition Document

  9. Rick Kazman, Mark Klein, Paul Clements, ATAM: Method for Architecture Evaluation, TECHNICAL REPORT CMU/SEI-2000-TR-004 ESC-TR-2000-004

  10. SKA-TEL-SKO-0001772 SKA Software Product Quality Assurance Plan

  11. SKA-GOV-HR00028 Code of Ethics

Standards Applicable to all SKA Software

  1. All SKA software shall have a copyright notice which is a description of who asserts the copyright over the software.

    1. Notes:

      1. Derived software and bespoke software will normally be comprised of code modules which have a mixture of copyright attributions. Some code modules will have joint copyright, and others have sole copyright, but the codebase in its entirety will have a mixture.

      2. Detailed guidelines on how to include Copyright information as part of bespoke software are published on the SKA developer portal [RD6] at Licensing a project.

  2. All SKA software shall have a software license which is a legal instrument governing the use or redistribution of software.

    1. Notes:

      1. The software license shall be delivered as part of all software products.

      2. Off-the-shelf software will normally have licenses over which the SKA has no control.

      3. Derived software may have a mixture of licenses.

      4. Bespoke software will normally have a permissive open source license.

      5. Detailed guidelines on how to include License information in a software distribution are published on the SKA Developer Portal [RD6] Licensing a project.

  3. All SKA Software shall be documented. The only official documentation language accepted by SKA is the English language.

    1. Notes:

      1. All SKA software documentation will include a user manual.

      2. Bespoke software and Derived software documentation will include developer documentation.

      3. Bespoke software and Derived software shall contain inline code documentation. Inline code documentation shall be written in English.

      4. All documentation and code shall be written so as to abide by the SKA Code of Ethics [RD11].

  4. The documentation associated with SKA software shall also be subject to a specific license unless it is covered by the software license.

  5. All software licenses governing a body of software must be mutually compatible.

  6. All software licenses for SKA software shall be agreed with the SKA Observatory prior to the software being adopted or developed.

    1. Notes:

      1. The license shall be agreed with the SKA Head of Computing and Software or their delegate as agreed.

      2. The SKAO will always agree to a 3 clause BSD license for software (provided there are no compatibility issues) and will favour open-source permissive licenses with attribution since they minimize compatibility issues.

      3. The SKAO will always agree to a Creative Commons Attribution 4.0 International License for documentation (provided there are no compatibility issues).

      4. This permissive open source recommendation is in line with the SKAO IP policy [AD1].

      5. It is understood that the IP licensing environment of FPGA software is often substantially different to that of the open source software environment, with many (or most) developments relying on IP (from the FPGA vendor, for example) that has more restrictive licensing. In accordance with this standard, use of this IP, and its associated license, must be agreed in writing with the SKA Observatory.

Standards applicable to Off-the-shelf software

All SKA Software which is off-the-shelf software shall have:

  1. A business case describing the requirements for the software, in comparison to other software.

  2. A record of the evidence that demonstrates that the software meets these requirements.

  3. A description of how the software will be supported during the expected lifetime of the software.

    1. Notes:

      1. The SKA Observatory has a predicted lifetime of 50 years, which is much longer than most software products and the companies that develop them. Hence this description may include: how many alternatives exist which also support the software’s data products, escrow agreements and commercial soundness of the company. Support includes:

        1. Managing unexpected behaviour of the software that is incompatible with the SKA Observatory’s (possibly evolving) requirements.

        2. Managing the evolution of underlying systems, such as hardware and operating systems, that the software depends on.

        3. Managing changes to the existing supplier support arrangements (e.g. the original company being acquired, the product becoming not commercially viable etc.).

        4. provides a lifecycle plan including isolation and integration within the intended solution architecture, and the process for decommissioning and succession.

      2. Software shall be delivered inclusive of all necessary information to perform a full reconfiguration of the software product deployment and configuration. This includes original binary installation files; any scripts that support code packaging, deployment, database migration and environment provisioning; all project artefacts (deployment procedures, release notes, etc…); all configuration files; and any other scripts or configuration information required to create infrastructure that supports multiple services (e.g. enterprise service buses, database management systems, DNS zone files, configuration rules for firewalls, and other networking devices).

  4. Evidence that the software has been developed to a standard of quality appropriate to the needs of the SKAO.

  5. Documentation that is appropriate to the needs of the SKAO. The only accepted language for software documentation is English.

  6. Where the software is expected to interoperate with other software packages, it shall expose integration points via a set of programmable APIs. Such interface shall be documented, accessible to SKA, and delivered as part of the software.

  7. Where the off-the-shelf softwareis expected to interoperate with other SKA Software, an instance of the software shall be available for installation in the various Integration and qualification environments so that SKA Software can be tested against it during development and integration phases.

  8. Been approved by the SKAO as to its fitness for purpose and included in a public register of approved SKA Software.

Standards applicable to derived software

As described in Scope of the document the spectrum between off-the-shelf software and bespoke software is a continuum and the application of off-the-shelf or bespoke standards will be evaluated on a case by case basis.

It is anticipated that SKA will make use of a number of domain specific open-source software packages, often developed in the context of the larger astronomy software ecosystem. A model for collaboration shall be established on a case by case basis, based on these criteria:

  1. The compatibility of the license applied to derived software shall be evaluated.

  2. Where an external open source software package is supported by a healthy community of developers, according to well established processes that enable collaboration, SKAO will encourage that interaction is carried on within the external software community.

  3. Where a software package needs to be adopted by SKA and supported mainly by the SKA development activity, it is preferred that the software is transferred under the SKAO. A greater part of the bespoke software standards will be applied in this case, with exceptions defined based on the status of the package on a case by case basis.

Standards Applicable to Bespoke Software


This section comprises standards relating to processes described by ISO 12207 [RD1], §7.1.2 (Requirements), §7.1.3 (Architecture) and §7.1.4 (Detailed Design). They complement any general System Engineering level standards described in the Engineering Management Plan [RD7] applicable to all SKA systems.

All SKA Software that is bespoke software shall have documentation and models covering the following:

  1. The requirements the software is intended to fulfil, in a way that can be traced to the higher-level SKA Requirements..

  2. The software architecture used.

    1. Notes:

      1. The software architecture must be documented as part of the SKA Solution Intent [RD8], published on the SKA Confluence website.

      2. The recommended reference for architecture documentation is “Documenting Software Architectures: Views and Beyond, Second Edition” (Clements et al, 2011) [RD2]. This book should be consulted for best practices on documenting views, styles and interfaces. The ISO 42010 [RD3] standard is also relevant.

      3. The architecture documentation should include, at minimum

        1. System Overview, including a description of the architectural styles used.

        2. A set of views describing key features of the architecture, and the mapping between views.

        3. Interface Documentation or references to applicable Interface Control Documents for the major interfaces.

        4. Rationale justifying how the architecture satisfies the system quality attributes and architecturally significant functional requirements. Justification on the basis of models and evolutionary prototypes is highly recommended in many cases.

        5. A consideration as to whether there is any existing software that meets, or can be modified to meet, the requirements.

      4. Emphasis should be on clear, unambiguous diagrams with accompanying descriptions and tables.

      5. Refer to Chapter 11 of Clements et al for a description of interface documentation. Interfaces that are language or framework specific may be best documented in a format appropriate to that language or framework (e.g. generated from comments and code in an evolutionary prototype).

  3. Where a prototype software exists that informs the development, evidence that such prototype software satisfies the architecturally relevant requirements.

  4. Detailed design of components.

    1. Note:

      1. It is expected that a significant amount of the detailed design may be automatically generated from code and comments. Detailed design information that can be derived directly from source code repositories is published as part of the SKA developer portal [RD6] at Documenting a project.

      2. Detailed design documentation for FPGA software should include estimates of device utilization (DSPs, BRAMS, LUTs etc), details of clock rates and clocking domains and tracking of timing closure issues

The software design should be reviewed, and the reviews should incorporate the following factors:

  1. The SKAO is responsible for reviewing and agreeing all system requirements.

  2. Specifications for the software will be accessible via the SKA Solution Intent Confluence Space:

    1. Notes

      1. SKA Requirements will be accessible via linkage with the Jama contour tool.

      2. Non-functional requirements are part of the specifications.

      3. The Architectural Decision Records (ADRs) are part of the specification. The related collection and analysis process is defined in the SKA developer portal [RD6] at doc:/policies/decision-making.

  3. SKAO personnel should be involved in software architecture reviews.

  4. The software architecture should be reviewed to demonstrate that it meets key requirements and provides sufficient detail for cost estimation and implementation.

    1. Notes:

      1. The Architecture Tradeoff Analysis Method [RD9] is a relevant process to be considered when executing software architecture reviews

  5. Both the architecture and detailed design reviews shall carefully consider the requirements relating to the long lifetime of the SKA Observatory. This includes, for example:

    1. Portability of the system across multiple architectures and operating systems.

    2. Consideration of the life-cycle of all dependencies, including development tools and run-time dependencies.

    3. The need for the system to be compatible with version 6 of the Internet Protocol.

    4. The careful design of API’s and the need to exchange data by API’s rather than relying on environmental assumptions about file systems, for example.

  6. Detailed design shall be reviewed:

    1. By someone in addition to the principal developer of the module being considered.

    2. In a manner appropriate to the significance of the module.

      1. Note:

        1. The significance of the code relates to the impact any changes to the design has on other parts of the system.

        2. The review process must not be overly bureaucratic. Development teams should be empowered to design and develop the code efficiently and modify the internal design when required.


This section comprises standards relating to processes described by ISO 12207 (2008) §7.1.5 (Construction).

The construction of SKA Softwarewhich isbespoke softwareis managed according to the SAFe framework, and it follows the quality processes described in the SKA Software Product Quality Assurance Plan [RD10].

The construction of all SKA Software which is bespoke software shall include:

  1. The construction of all source code shall follow a defined documented process that is approved by the SKAO.

    1. Note:

      1. The process documentation shall include a workflow description that follows accepted best practices. For example, it is recommended that:

        1. Work management practices shall include the following:

          1. All work tasks shall be described in a ticketing system.

          2. Work tickets shall have a description of the task, an estimate of the resource required and amount of the task that has been completed.

          3. All code commits shall relate to a ticket in the ticketing system.

          4. The developing organisation shall be able to use the ticketing system to generate progress metrics.

        2. Code management practices shall include the following:

          1. With the exception of trivial cases (e.g. possibly minimal documentation changes) code must only be added to or merged with the default development branch by a merge-request-like 3 mechanism [RD6] (Working with GitLab).

          2. The merge request (or similar mechanism) must only be accepted after the code has been cleanly compiled and passes all appropriate tests. This process should be triggered automatically.

          3. Merge requests must only be accepted after the code changes have been reviewed by more than one developer (inclusive of the primary developer).

          4. Merge requests must only be accepted by suitably qualified individuals.

        3. Management of binary artefacts shall include the following:

          1. Binary artefacts such as container images and software packages are generated in a way that is automated, traceable, and reproducible. See Software Package Release Procedure in [RD6] for details.

          2. Binary artefacts are made available during the development activity at relevant stages for integration purposes.

  2. All construction software development shall utilise an SKAO approved version control system.

    1. Note:

      1. The SKAO approved version control system is Git.

  3. All documentation, source code, software source code, firmware source code, HDL source code, unit tests, build scripts, deployment scripts, testing utilities and debugging utilities must reside in the version control system. More detailed guidance on what to include in each software repository can be found on the SKA developer portal [RD6] at Create a new project.

    1. Note:

      1. To the maximum extent everything stored in the version control system, including for example firmware source code, shall be stored in a portable/non-proprietary format.

  4. Release tags for code shall adhere to the Semantic Versioning 2.0.0 specification [RD5].

  5. Software shall be written in an SKA approved language and adhere to SKA language specific style guides.

    1. Note:

      1. The primary approved language shall be Python.

      2. Coding guidelines and standards for each programming language are maintained on the SKA developer portal [RD6] at Coding guidelines.

      3. Use of other languages must be justified by, for example:

        1. Impossibility of running Python in the chosen run-time environment.

        2. Python doesn’t provide the necessary performance or a native language extension is not feasible.

      4. Many other languages are likely to have extensive usage. For example:

        1. C/C++ (for high performance computation on conventional CPU’s).

        2. Java (e.g. for business logic in web systems and derived software).

        3. VHDL (for FPGA development).

        4. CUDA (for GPU software).

        5. OpenCL (for software that targets both GPU and FPGAs)

        6. JavaScript (for Web client systems).

  6. SKAO employees must have access to the repository while the software is under development, be able to sign-up for notifications of commits and, if necessary, give feedback to the developers.

  7. Test software verifying the system software at multiple levels (from the complete system down to individual module unit tests). Tests shall include verifying specific requirements at different levels and, as far as practicable, be able to be run automatically.

    1. Note:

      1. Tests shall be able to run in a continuous integration environment.

      2. The SKA testing policy and guidelines are published on the SKA developer portal [RD6] at Software Testing Policy and Strategy and those shall be followed by software development teams.

      3. For software targeting CPU’s this should include unit tests at the class, function or source file level to test basic functionality of methods (functions) with an agreed minimal coverage of at least 75%, as per the SKA Definition of Done [RD6] ( Definition of Done ). Unit tests created for fixing defects or making specific enhancements should be checked-in with a reference to the issue for which the tests were created.

      4. For FPGA software this should include:

        1. Each module shall be associated with a specific test bench.

        2. Modules shall undergo simulation with a predefined pass/fail criteria.

        3. Release builds shall be made up of verified functional blocks and handled in a scripted framework.

        4. Simulated and released code shall match the committed code. For example, committing the code shall not change register contents (even version numbers) in the source code.

  8. Software simulations/stubs/drivers/mocks for all major interfaces to enable sub-system and system level tests.

  9. Automated documentation generation - including, but not limited to parts of detailed design documentation.

    1. Note:

      1. Automated documentation generation software is generally off-the-shelf software and so subject to the conditions in section 4.

      2. Not all documentation can be automatically generated, but it should be used wherever it is reasonably practicable.

      3. The SKAO shall accept ReST format documentation generated using Sphinx.

  10. A complete definition of other software (both off-the-shelf and bespoke) that the software requires to build and deploy.

  11. Deployment scripts or configurations, which allow the software to be deployed cleanly and in as automated a fashion as is practicable, starting with a bare deployment environment.

    1. Note:

      1. For FPGA software, this means configuring an un-programmed FPGA device in the target SKA system. Deployment may require the use of the host-based software delivered as part of the control system. In that case, that software also needs to be delivered to SKA under the same conditions of the FPGA software.

  12. The ability to log diagnostic information according to the Logging Standards described in the SKA developer portal [RD6] SKA Log Message Format.

  13. The ability, dynamically at runtime, to suppress or select logging of messages at different severity levels on at least a per-process basis (and a per-thread basis or per class basis if appropriate).

  14. Applications must observe the POSIX conventions for IO on the standard streams stdin(0), stdout(1), and stderr(2).

  15. The use of process exit status codes must reserve 0 for success and treat any other value as an error condition.

  16. Process must observe the POSIX conventions for responding to signals especially SIGTERM (terminate gracefully), SIGINT (interrupt and exit), and SIGHUP (terminate or reload).

  17. The ability to log diagnostics at all major interfaces at a Debug severity level according to the Logging Standards described in the SKA developer portal [RD6] at SKA Log Message Format.

  18. Alarms, where applicable, shall be based on the IEC 62682 standard [RD4].

Acceptance and handover

This section comprises standards relating to processes described by ISO 12207 [RD1], §6.4.8 (Acceptance Support), §7.1.6 (Integration) and §7.1.7 (Qualification).

The acceptance and handover of SKA Softwarewhich isbespoke softwareis managed according to the SAFe framework, and it follows the quality processes described in the SKA Software Product Quality Assurance Plan [RD10].

SKA software which is bespoke software will only be accepted by the SKAO after it has been appropriately integrated, verified and validated.

  1. The integration, verification, validation and acceptance of all source code shall follow a defined documented process that is approved by the SKAO.

  2. This process must make clear, for all times during the handover:

    1. Who is responsible for making software changes.

    2. What the expected turnaround time for software changes is.

  3. At the completion of the process all code shall have been:

    1. shown to pass appropriate, system, sub-system and unit level tests.

    2. shown to cleanly compile and/or build using an SKAO provided build environment.

    3. checked into an approved SKAO artefact repository.

  4. Software shall be integrated, as far as possible, prior to the integration of other aspects of the system.

    1. Note:

      1. Where possible, software shall be integrated continuously, starting from the earliest development stages [RD7].

      2. During the SKA construction, this means that it is intended for this to take place in advance of the SKA Array Release schedule.

      3. The Continuous Integration pipeline will integrate and progressively promote software through increasingly stringent qualification environments [RD7].

  5. When the SKAO takes over maintenance of the software the complete repository, including commit history, shall be delivered to the SKAO.

  6. Where code requires specialised hardware for testing, provision of this hardware, or demonstrably equivalent hardware, shall be included as part of the handover. Such hardware must be demonstrated to be in good working, serviced condition and provided with documentation and relevant service-level arrangements.

Support Infrastructure

To develop and integrate software the SKAO shall provide:

  1. A central, globally visible, set of repositories that can be used by all SKA developers.

    1. Note:

      1. SKA has chosen the Gitlab 4 platform to host and manage the source code repositories.

      2. Usage of software repositories from developers is regulated according to the processes described on the SKA developer portal [RD6].

      3. These repositories will clearly define how to handle large binary data files.

  2. A globally accessible website for the storage and access of documentation.

    1. Note

      1. The SKA has chosen the Readthedocs 5 publishing platform to publicly make available all code documentation.

      2. How to connect software repositories with the publishing platform is documented in the SKA developer portal [RD6] at Documenting a project.

  3. A continuous integration and test framework that is open to use by developers.

    1. Note:

      1. The SKA has chosen the Gitlab platform to manage the Continuous Integration of software products. The SKA developer portal described the process to make use of this infrastructure.

      2. It is intended that this will include support for at least the 4 types of bespoke software described in the scope section (Tango, SDP and NIP data driven software, FPGA software and Web Applications).

      3. The development of this will be done in conjunction with the pre-construction and construction consortia. The SKAO will serve as an overall coordinator.

  4. Communication tools to manage the software development activity and to enable software developers to access expertise from all the SKA software developer community.

    1. Note:

      1. SKA has chosen to adopt Jira 6 and Confluence 7 collaboration tools to manage the software development activity. All contributors to SKA software, including manager and developers, will have an account on these platforms.

      2. SKA will provide an instant messaging and presence awareness platform. All contributors to SKA software , from managers to developers, will have an account on such platforms.

      3. How to use the communication tools is documented as part of the SKA developer portal.

  5. A list of approved off-the-shelf software.

    1. Note:

      1. Corporate off-the-shelf software is approved for use by the SKA Head of IT and a list of available software is maintained on the SKA Confluence website.

      2. Developer-oriented off-the-shelf software, often referred to as dependencies, to be used in the development of software for the construction of the SKA telescope is approved for use by the SKA Lead Software Architect and a list of available software is maintained on the SKA Artefact Repository and published on the SKA developer portal.

      3. The intention of this approved list is to aid standardisation.


From Wikipedia entry for “Hardware Description Language”, retrieved 25 January 2021. (


From ISO 12207[RD1],