In project management, there are typically 3 types of phase to phase relationships. All three are discussed in detail below,

1. Sequential Relationship
Phases happen one after other and never overlap. An example could be the waterfall model
2. Overlapping Relationship
Phases overlap with each other. There are typically separate teams working on the separate phases. An example is below,

3. Iterative Relationship
This kind of relationship is a cross between sequential and overlapping relationships. This is typically used for Agile software development. As opposed to the overlapping relationship, this has only 1 team working on both phases. What that basically means is for one phase the project team could be working on Initiation/Planning while for another phase they could be working on Execution/Closure

These three are the very basis of all the different types of project management life cycles
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