How to Use this Site
Q42 helps you specify quality requirements for your system. The site uses five connected concepts: dimensions, characteristics, requirements, approaches, and standards.
Our Domain Language
Let’s explain some terms, starting with an example:
- #secure is a quality dimension (others could be #flexible or #reliable).
- Confidentiality is a quality characteristic, refining the dimension.
- “Sensitive data must not be accessible if storage is compromised: No (0%, zero) unencrypted sensitive data on persistent storage” is a quality requirement with precise Metric for this characteristic.
- ISO/IEC 27001 is a quality-related standard calling for confidentiality.
- “Encrypted in-memory caching with short TTL” could be one approach to achieve or improve the quality requirement.
- Once all approaches are implemented, confidentiality (as detailed by the requirements) becomes a quality attribute of the concrete system.
Now let’s consider the terms in more detail:
| Term | Icon | Explanation |
|---|---|---|
| Dimension | Our top-level dimensions (#flexible, #maintainable, #efficient, #reliable etc.). Find the full list plus the mapping to qualities here. These terms are abstract, and will be interpreted individually by different stakeholders. They can be used as starting points, but need to be detailed. Q42 relates each of these dimensions to 10-30+ different specific quality characteristics. The dimensions intentionally overlap and are not orthogonal. | |
| Specific Quality Characteristic | The detailed and specific terms, like accessibility, accountability, accuracy etc. Currently, Q42 collects more than 180 such terms under Quality Characteristics. These terms are usually well-defined, but need examples or acceptance criteria to really help in developing systems. Q42 contains examples for many (hopefully all, at some day in the future) | |
| Stakeholder | People, roles or organizations that need, want or require certain quality requirements for their systems. | |
| Examples | These are the specific requirements stakeholders have for a system or product, often expressed in the form of quality scenarios. They should facilitate stakeholder communication by enabling a common understanding of the good enough. Q42 provides >50 of these examples | |
| Acceptance criterion | What does good enough mean with respect to a specific quality. | |
| Approach | Under development, consider this content experimental: How to achieve one or several qualities. | |
| Standard | Numerous international standards describe/prescribe/care about certain aspects of quality. Important ones are ISO-25000:2023, ISO-27001 or MISRA. |
Three Axis of Quality
- Axis 1: Dimensions & Characteristics
- What characteristics, attributes, properties or dimensions are relevant (like availability, latency, speed or maintainability). On this site, we use the color blue to denote quality dimensions and characteristics.
- Axis 2: Acceptance Criteria
- What amount, size or extent of any characteristic (like 99% availability...). We use the colour red for these criteria, metrics, acceptance criteria or examples.
- Axis 3: Stakeholder
- For whom or what roles/organizations is this quality or requirement relevant?
How to Use Q42
You can approach in several ways:
- Inside-out, starting with the top-level dimensions
- Outside-in, by reading through the extensive list of quality characteristics.
- By asking your stakeholders for terms (either dimensions or specific quality characteristics) they consider important, and then continue with steps 1 or 2.
- By reading the examples of quality requirements.
All these approaches are described below.
Inside-Out, starting with Q42 Quality Dimensions
Let’s assume that your stakeholders want a “flexible” system. This is completely unsuitable as a requirement because it is too unspecific.
You could search under the term “#flexible” (to be found under “Quality Dimensions”). There you find a collection of related terms (“Qualities tagged with #flexible”), and also a collection of exemplary quality requirements of this generic term.
Outside-In
The other way round is viable, too: In case your stakeholders have specific requirements, like “compliance”: Just start with the (extensive!) list of qualities.
Again, you will find related qualities and examples on the detail-pages
Start with Examples
The third option starts with the examples of specific requirements. These are automatically mapped to the dimensions and quality characteristics.