Formalize linking between `ConnectionStrategy` output, and `ConnectivitySet` naming.

[Helveg]

Currently, the convention is to name a ConnectionSet after the ConnectionStrategy. If there are multiple cell types involved, and the ConnectionStrategy does not give a specific tag to name the set, a {base}_{pre_ct_name}_to_{post_ct_name} convention is used, where base is the conn strat name.

If we want to have a predictable link between a connection strategy and the connection sets it will produce, an optional output_naming attribute to the base ConnectionStrategy. The options are:

• Not specified: The default convention is used, base = conn strat name
• A single string: A different base is used
• A list of strings: Treat each item in the list as a base, and merge all output names.
• A double map is given from to to:
  • Every from-to pair that appears in the map is overridden by the key.
  • Each value can also be an array, specifying that multiple from-to sets for the same cell types will be produced
  • Each value can be null, specifying that this pair of cells will not produce any output connections
  • Combinations that don't appear follow the default convention
  • Combinations that don't exist raise ConfigurationError
• Calls to strategy.connect_cells with a tag= kwarg that isn't corroborated by the output naming is rejected.
• A new function get_output_names will be added to the base strategy class
  • A component can override it
  • Will be called with the cell type pair, to get its output name:
  • If an array is returned, tag must be specified.
  • if a single value is returned tag is optional, and when given must match the value exactly.
  • When called without arguments must return all possible output names
  • When cell types are input that aren't part of the connection strategy, it should ValueError.
  • When a null value is encountered it should return None

Examples

SIngle cell convention

wow:
  strategy: my_very_wow_strategy
  presynaptic:
    cell_types:
      - A
  postsynaptic:
    cell_types:
      - C

would allow the following connection set tags: wow.

Setting output_naming: different would yield different. Setting output_naming: [x, y] would yield [x, y]

Default convention

wow:
  strategy: my_very_wow_strategy
  presynaptic:
    cell_types:
      - A
      - B
  postsynaptic:
    cell_types:
      - C
      - D

would allow the following connection set tags: wow_A_to_C, wow_A_to_D, wow_B_to_C, wow_B_to_D.

Setting output_naming: different changes each occurence of wow in the above tags to different. Setting output_naming: [x, y] would yield 8 labels, 4 with x_* and 4 with y_*.

Others

wow:
  strategy: my_very_wow_strategy
  presynaptic:
    cell_types:
      - A
      - B
  postsynaptic:
    cell_types:
      - C
      - D
      - E
  output:
    - A:
      - C: wow_A_to_C
      - D: A_to_D
    - B:
      - C: ["B_to_C:type_1", "B_to_C:type_2", "anomalies"]
      - D: null

would allow the following connection set tags: wow_A_to_C, wow_A_to_D, wow_A_to_E (implicitly), B_to_C:type_1, B_to_C:type_2, anomalies, (B to D is disabled), wow_B_to_E (implicitly)