Engineering plan for restructuring software architecture of bayeslite

[fsaad]

Internal software and user facing language will be undergoing a dramatic
makeover.

The changes outlined in this ticket:

• will be completely backwards incompatible
• will render any existing bdb unusable
• will break all existing clients of bayeslite
• will render any existing BQL/MML documentation out of date

Removing 'metamodel' concept in favor of 'backend'

• Rename interface of IBayesDBMetamodel to IBayesDB_Backend
• Expunge all instances of "metamodel" in the source code.
• Expunge metamodels.crosscat.CrosscatMetamodel
  • Remove all tests which target the internals of CrosscatMetamodel.
  • Replace all bql compiler tests using CrosscatMetamodel to use
    CGPM_Metamodel.

Merge tables, populations, generators, into one concept

• Remove CREATE POPULATION p FOR t
• Add CREATE POPULATION p FROM 'path'
  • Creates sqlite table p which is the base table of bayesdb population p.
• Add CREATE POPULATION p FROM "t"
  • Creates sqlite table p (as a clone of t) which is base table of bayesdb
    population p.
• Remove GENERATOR g FOR p.
• Merge notions generator_id in favor of population_id given the 1-1
  correspondence.
  • Replace generator_id with population_id in IBayesDB_Backend.
  • Replace all generator methods in core to population.
  • Remove all unused generator methods.
  • Remove generator_id from all methods which take in a population_id.
• Move stattype guessing/management from bayeslite into each backend.
  • bayeslite provides a table to each backend to store its stattypes.
  • create_generator (to be create_population) in runtime should place
    entries said table.
• Remove aggregation over metamodels bqlfn.py.
• Remove MODELED BY from BQL grammar.

Updates to compiler and bqlfn

• Remove all generator_id parameters from bqlfn
• Remove all generator_id arguments written in compiler.

Clear up several items in the main schema.py

• Merge bayesdb_generator_column with bayesdb_population_column (#443)
• Merge bayesdb_generator with bayesdb_population
• Remove bayesdb_generator_column
• Rename bayesdb_generator_model to bayesdb_population_model
• Remove bayesdb_session
• Remove bayesdb_session_entries
• Remove bayesdb_stattype
• Simplify bayesdb_variable to exclude generator_id

Simplify population schema definition.

• GUESS STATTYPES OF (*);
• SET STATTYPES OF to
• Remove CATEGORICAL in favor of NOMINAL.
  • Rationale: An ORDINAL variable is conceivable CATEGORICAL, where there is an
    ordering among the discrete categories.

Simplify half-implemented or confusing features

• Remove codebook.py
• Merge "similarity" with "predictive relevance".
  • Remove the "multi-row" aspect; effect can be achieved using SQL.
  • Raise error if more than one matching row exists.
  • Allow hypothetical rows for a "similarity" query.
• Remove WAIT from BQL ANALYZE.
• Remove checkpoint by seconds?
  • wontfix.
• Remove ANALYSIS SCHEMA / ANALSYES.
• Remove WITH BASELINE syntax (created for ephemeral purposes).

Ad-hoc issues

• cgpm_metamodel.analyze needs to capture None iterations/seconds and
  return.
• cgpm_metamodel._merge_user_constraints needs to capture None case.
• cgpm_metamodel alter requires dependent for all columns only (easy to fix
  now, post panelcat).
  • Issue in test_bql.test_conditional_probability, but was easily handled.
  • We should still support the more general dependency case now that we have
    fixed column transitions to be ergodic in lovcat, created ticket #592.
• cgpm_metamodel returns 'TypeError: expected string or buffer' when there
  are no initialized models. Came up in test_core.test_bql for "analyze pe_cc
  for 1 iteration wait".
• cgpm_metamodel checkpoint seconds raises NotImplementedError instead of
  BQLError.
• cgpm_metamodel does not store iterations in bayesdb_generator_model.
  test_bql.test_checkpoint__ci_slow.
  • Removed the iterations column from bayesdb_generator_model; tracking
    model analysis statistics is a backend-specific operation not the concern
    of anything in schema.py.
• cgpm_metamodel returns an error if trying to simulate a constrained
  column; appeared in test_simulate.test_simulate_drawconstraint_error.
  • Made 1 test case be an error, another test case be a valid simulation.
• cgpm_metamodel accepts constraints for unseen nominals. This came up in
  test_codebook. Changed to make sure densities agree.
• engine caching mechanism is not compatible with sqlite rollbacks. Issue
  discovered in test_metamodels. See CGPM_Metamodel._engine_latest for
  discussion and workaround.
• Move src/backends/crosscat_theta.schema.json to probcomp/crosscat.
• Move notes/crosscat-schema.txt to probcomp/crosscat.

Related tickets that will be resolved:
#284
#388
#427
#441
#443
#467
#469
#562

[fsaad]

d2376c1

Above merge commit contains a partial resolution of this ticket, clearing out roughly 50% of the work items. This commit is considered stable, and all unchecked issues in the list above are considered on hold until further notice.

[fsaad]

The unchecked items under heading "Merge tables, populations, generators, into one concept" have been mostly addressed by a user-facing workaround per #596, which keeps the full generality of the existing system while allowing "implicit" populations/generators that inherit names from their bases tables/populations.