The purpose of the specifications and the product backlog is to ensure that the final deliverable meets the needs of the customer or end user as closely as possible. It is therefore used to identify customer requirements and to structure the work to be done to achieve the final deliverable.

So it’s the same thing, but it’s very different!

What differences are there?

REQUIREMENTS SPECIFICATION

• Origin. The term “specifications” originated in the Middle Ages in the field of construction and engineering. Project owners (architects, engineers) wrote down their requirements, their “specifications”, on sheets of paper and passed them on to the craftsmen. All these sheets together formed a “notebook”.
• How it is used. It serves as a reference for defining the customer’s or client’s expectations of the deliverable. It is the responsibility of an expert or the person in charge of managing the project.
• Content. The requirements specification detail the constraints and functional requirements of the deliverable, as well as the associated performance criteria.
• Evolution. The requirements specification is a formal, static document, once it has been accepted during the planning phase. Any changes are subject to a formal validation process, which is not very flexible.

PRODUCT BACKLOG

• Origin. The expression “product backlog” is an Anglicism originating from agile methodology, in particular Scrum. The word “backlog” literally means accumulation, delay and represents a list of tasks or items awaiting processing.
• How is it used. It is used to organise and prioritise the work to be carried out on the deliverable. It is constantly updated to reflect the changing needs of the product. It is the responsibility of the “product manager”.
• Content. The product backlog is made up of “customer stories”, which represent the functionality of the deliverable expected by the customer, as well as elements representing improvements or corrections to be made to the deliverable.
• Evolution. It is potentially updated during each iteration, or sprint, of the agile process, depending on customer feedback and changes in priority.

In short, the specification is a static document that specifies the requirements of a deliverable, whereas the product backlog is a dynamic, evolving list representing the tasks to be carried out as part of an agile development process. In both cases, it is the document that frames the development of the deliverable, ensuring that its final form perfectly meets the customer’s needs.