In a project, what is the relationship between dependent tasks called?

If I have two tasks, called "Design" and "Development", what are the relationships between the two called?

Clearly, this is a type of dependency, but I need to be more specific.

That is, I need to be able to say:

In this relationship, "Design" is the A and "Development" is the B

My wife and I have been discussing this for quite some time now, and here are the few we have come up with, and why they don't work for me:

• Depender/Dependee
  Feels awkward, and doesn't really disambiguate the parties involved. Also implies that the dependee provides something to the depender, whereas this is not necessarily always the case in project tasks.
  
  
• Dependent/Surrogate
  Awkward and implies providing some sort of utility.
  
  
• Parent/Child
  Incorrect. The "Design" task may have children tasks, like "Write-up" or "Gather Requirements", but "Development" is not a child of "Design".
  
  
• Predecessor, Precursor, etc. / Successor
  Has hierarchy implications that make it quasi-incorrect.

So, the best we have right now is:

• Prerequisite/???
  Project tasks are related in exactly the same way that some educational courses are. This does imply providing some sort of utility, but not necessarily and the relationship is well understood.

Solution 1:

Prerequisite - Co-requisite - Post-requisite -- Where task A is the prerequisite and task B can either be a co-requisite or post-requisite.

As a project manager I have often used predecessor/successor, but usually where there is a chronological order.

Project tasks are related in exactly the same way that some educational courses are. This does imply providing some sort of utility, but not necessarily and the relationship is well understood.

With this in mind, one of my college chem classes was a prerequisite and an associated chem lab was a co-requisite.

Solution 2:

I thought "Prerequisite" as soon as I saw the example. As far as the inverse goes, the "B" in "Development is the B" portion of your question, I would propose a couple of terms:

• Product if A in whole or in part becomes B, as in the product of a chemical reaction.
• Dependent or Dependency if B just requires A to exist. In software, when program A relies upon the presence of program B, then "A is a dependency of B".

If you drop the "Prerequisite", you could use Predecessor / Successor, which states only that A comes before B.