SDB ToDo list (and general notes)
=================================

+ Tranasactions - cleanup.
+ Graph => Quad
+ Graph => Tuple loader.

+ Tuple loader

+ QueryEngineSDB has duplication with QueryEngineMain - eliminate!

+ TableDesc - better table description system
  Partly done: The formatters still know the column names.
  See index/FmtDerby

+ Pattern/Inf tables:
  Data:
    Q: { :s a ?t }  D: :s a :C1 . :s a :C2 .  : SC: (:C1, :C2) => duplicates
  Reduce data?  is there always a minimum?  No - but synthetic?
  Or nestes SELECT DISTINCT in SQL.

+ Store config
    in sdb.ttl // in DB // rebuildable?
    Current description + "features"

+ StoreFactory : have an open registry.

+ StoreConnection needs a StoreLayout indirection ??
  + to get table names for formatting
  + to get the layout subtypes (1/2 ; index/hash ; triples/quads)
  Connection -> Config "StoreControl" -> Store 
  Store hasA "StoreControl" -- c.f. StoreFormatter
   Features play into this

  StoreConfig is the in-DB mapping.
    Repurpose this name?

+ --sdb=@ for global registration?

+ Prefixes : disable for ModelRDB only.
  Done?? Check

+ Prepared statement query cache?
  When will it be beneficial - GraphSDB and add/delete single triples?

+ Value-based hashing
  String version - and have fixed choice of xsd:string or plain string for terms.
  Partial alternative: condition is "T.o = hash1 OR T.o = hash2"

+ Features: more general config setting?
  Or really use properties?
  layout; layout/index; layout/hash for now.

+ Generating SQL:
  + Precedence-driven output for SqlExpr // SqlExprGenerateSQL, not lots of nesting.
  + SELECT/one table ==> move constraints out (it's just SPJ)
    Put in a SqlNode optimizer stage, just before generation
      IJ-R-T => IJ(r)-T is done specially 
  + Generalize linearization of InnerJoin-only trees
  + Be careful about code generation and a right complex expression
    Use a SELECT for nested expressions?  generalize from COALESCE code generation.
    
+ Values and conditions : reactivate condition compilation.
  Need value access
  Isolate QC2.insertValueGetter

+ Add query tests :
  /Structure/ { opt ... } JOIN { opt ... } 
  
+ ValueTables
  String value table
    With no URIs, much shorter.
    Full text indexing where available?