What is the difference between technical specifications and design documents?

Question

What are technical specifications? Are they the same as design documents. If not, what is the difference and some examples?

Answer 1

A software design document can be at the level of a system or component, and generally includes:

• relevant goals or requirements (functional and non-functional);
• static structure (e.g., components, interfaces, dependencies);
• dynamic behavior (how components interacts);
• data models or external interfaces (external to the system/component described in the document); and
• deployment considerations (e.g., runtime requirements, third-party components).

Note that all of these descriptions are at an abstract level. The purpose is to give the reader a broad general understanding of the system or component. There may be many levels of design documents (e.g., system- or component-level).

A technical specification describes the minute detail of either all or specific parts of a design, such as:

• the signature of an interface, including all data types/structures required (input data types, output data types, exceptions);
• detailed class models including all methods, attributes, dependencies and associations;
• the specific algorithms that a component employs and how they work; and
• physical data models including attributes and types of each entity/data type.

Answer 2

Technical specifications, at least in the form of a technical design, are part of the design documents, along with, for example, requirements lists, functional designs, user stories, graphics design mockups, usability studies, UML diagrams, business process diagrams, data model specifications, etc.

Technical specifications of the type that you write after the fact, to document the finished product, are not generally part of the design documents, but they can be included in the set of design documents of a later version (for reference) or another product that relies on them.