5.5.1. Tool Requirements¶
To manage requirements some tool support is helpful. Here is a list of requirements for the tool:
The tool shall be open source.
The tool should be actively maintained during the initial phase of the RTEMS requirements specification.
The tool shall use plain text storage (no binary formats, no database).
The tool shall support version control via Git.
The tool should export the requirements in a human readable form using the Sphinx documentation framework.
The tool shall support traceability of requirements to items external to the tool.
The tool shall support traceability between requirements.
The tool shall support custom requirement attributes.
The tool should ensure that there are no cyclic dependencies between requirements.
The tool should provide an export to ReqIF.
5.5.2. Tool Evaluation¶
During an evaluation phase the following tools were considered:
The tools aNimble, OSRMT and Requirement Heap were not selected since they use a database. The tools Papyrus, ProR and ReqIF are Eclipse based and use complex XML files for data storage. They were difficult to use and lack good documentation/tutorials. The tools rmToo and Doorstop turned out to be the best candidates to manage requirements in the RTEMS Project. The Doorstop tool was selected as the first candidate mainly due a recommendation by an RTEMS user.
5.5.3. Best Available Tool - Doorstop¶
Doorstop is a requirements management tool. It has a modern, object-oriented and well-structured implementation in Python 3.6 under the LGPLv3 license. It uses a continuous integration build with style checkers, static analysis, documentation checks, code coverage, unit test and integration tests. In 2019, the project was actively maintained. Pull requests for minor improvements and new features were reviewed and integrated within days. Each requirement is contained in a single file in YAML format. Requirements are organized in documents and can be linked to each other [BA14].
Doorstop consists of three main parts
a stateless command line tool doorstop,
a file format with a pre-defined set of attributes (YAML), and
a primitive GUI tool (not intended to be used).
For RTEMS, its scope could be extended to manage specifications in general. The primary reason for a close consideration of Doorstop as the requirements management tool for the RTEMS Project was its data format which allows a high degree of customization. Doorstop uses a directed, acyclic graph (DAG) of items. The items are files in YAML format. Each item has a set of standard attributes (key-value pairs).
The use case for the standard attributes is requirements management. However, Doorstop is capable to manage custom attributes as well. We will heavily use custom attributes for the specification items. Enabling Doorstop to effectively use custom attributes was done specifically for the RTEMS Project in several patch sets which in the end turned out to be not enough to use Doorstop for the RTEMS Project.
A key feature of Doorstop is the fingerprint of items. For the RTEMS Project, the fingerprint hash algorithm was changed from MD5 to SHA256. In 2019, it can be considered cryptographically secure. The fingerprint should cover the normative values of an item, e.g. comments etc. are not included. The fingerprint would help RTEMS users to track the significant changes in the requirements (in contrast to all the changes visible in Git). As an example use case, a user may want to assign a project-specific status to specification items. This can be done with a table which contains columns for
the UID of the item,
the fingerprint, and
the project-specific status.
Given the source code of RTEMS (which includes the specification items) and this table, it can be determined which items are unchanged and which have another status (e.g. unknown, changed, etc.).
After some initial work with Doorstop some issues surfaced (#471). It turned out that Doorstop is not designed as a library and contains too much policy. This results in a lack of flexibility required for the RTEMS Project.
Its primary use case is requirements management. So, it has some standard attributes useful in this domain, like derived, header, level, normative, ref, reviewed, and text. However, we want to use it more generally for specification items and these attributes make not always sense. Having them in every item is just overhead and may cause confusion.
The links cannot have custom attributes, e.g. role, enabled-by. With link-specific attributes you could have multiple DAGs formed up by the same set of items.
Inside a document (directory) items are supposed to have a common type (set of attributes). We would like to store at a hierarchy level also distinct specializations.
The verification of the items is quite limited. We need verification with type-based rules.
The UIDs in combination with the document hierarchy lead to duplication, e.g. a/b/c/a-b-c-d.yml. You have the path (a/b/c) also in the file name (a-b-c). You cannot have relative UIDs in links (e.g. ../parent-req) . The specification items may contain multiple requirements, e.g. min/max attributes. There is no way to identify them.
The links are ordered by Doorstop alphabetically by UID. For some applications, it would be better to use the order specified by the user. For example, we want to use specification items for a new build system. Here it is handy if you can express things like this: A is composed of B and C. Build B before C.
5.5.4. Custom Requirements Management Tool¶
No requirements management tool was available that fits the need of the RTEMS Qualification Project. The decision was to develop a custom requirements management tool written in Python 3.6 or later. The design for it is heavily inspired by Doorstop.