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# Terminology

## Scheduling

Scheduling observations is a common task in astronomy, but there is a lack of formal terminology. Here we define the terminology as it will be used in astroplan for scheduling tasks. This is for consistency within the code and the documentation.

The terms used are as follows:

- observing block (OB): an observation of a target for an amount of time and a particular instrument configuration.

- priority: number assigned to the observing block by the user that defines its precedence within the set of blocks to be scheduled. Should probably also be on a 0->1 (0=no good, 1=good) scale, or rescaled within the scheduler

- rank: like a priority, but defined for a specific set of OB**s, often set by an agent other than the observer. (e.g. a proposal is **ranked by a time allocation committee (TAC))

- constraint: sets limits and can yield scores based on inputs. Currently only boolean scores are implemented in the code.

- score: the value returned by evaluating a constraint or constraints. Can be boolean or floats between 0 and 1 inclusive (0=no good, 1=good), with a flag in the `Constraint` call that selects which is used. Can be combined by a scorekeeper into a cumulative score for an observing block given a start time.

- scorekeeper: assigns a cumulative score to the OB based on some function that would be applied to all the individual scores (result should be in (0, 1))

- scheduler: the entity that consumes the results of the scorekeeper and the observing blocks and produces a schedule

- Weights (“user defined”?): preferences for which constraint’s scores matter most (e.g. I care more about getting dark time than getting a low airmass). weights can be floats between 0 and 1 inclusive (0=not important, 1 = important)

This is a list of possible schedulers, none are implemented yet. Once implemented they will have different methods for creating their schedule. Below is a list of ideas for the scheduler descriptors and the related scheduler would work. Each scheduler will be able to be called with `DescriptorScheduler(args)` using the descriptor defined below.

- Sequential: starts from the beginning of the time range and schedules the OB with the best score, that hasn’t already been scheduled, for that time.

- Priority: starts from the highest priority OB and schedules it at the time where it has its highest score. Then schedules the next-highest priority without overlapping blocks