AtomSpace-SQL DB Bridge

The bridge connects pre-existing SQL DB's to the AtomSpace, so that data can move between the two, in both directions. It is meant to allow the AtomSpace to access foreign, external data, and manipulate it using the AtomSpace software stack. This is not intended for generic save/restore of AtomSpace contents. For that, see the native atomspace-rocks RocksDB StorageNode and the atomspace-cog network StorageNode.

The following are desired features:

• Automatic creation of maps from the SQL tables to AtomSpace structures. Fully automated, by importing pre-existing SQL table schemas. Optionally, this can be overloaded with custom templates.
• Custom mappings or templates would allow more "natural" Atomese representations. Complex SQL systems tend to have ugly, convoluted table structures with complex primary-key/foreign-key interactions. It would be nice to hide this in the AtomSpace mapping, so that we don't import the grunge and cruft of the SQL table designs.
• The bridge should allow both the read and the update of the contents (rows) in the SQL tables (while maintaining all foreign-key constraints during writing.)
• The bridge loads data incrementally. The bridge does not require a bulk import/export, but rather will access individual rows, columns and tables on an as-needed basis. This would allow the AtomSpace to work with datasets that are too big to fit in RAM.
• Adherence to the AtomSpace Sensory perception-action API for general agents.

At this time, only Postgres is supported.

Status

Version 0.2.1 -- The current implementation can load table descriptions and table contents from Postgres DB's. It can also load related rows and columns (rows and columns joined by a common column name). Two demos: a basic demo, showing the basic idea, and an ASCII table browser, allowing you to pilot around, bouncing from table to table, along joins. It's an ASCII browser because all of the graphical browsers for the AtomSpace have been neglected. (These: atomspace-explorer, atomspace-typescript and cogprotolab.)

History

Per request of Mike Duncan, Dec 2022. Map the FlyBase Drosophila Genome Database (current release here) into the AtomSpace, using the Chado schema given here.

Generic Mapping

Here's a sketch for a generic mapping. This could work for any SQL database.

For each row in some table tablename, create a conventional Atomese EdgeLink.

   Edge                      ; A single row in the table.
      Predicate "tablename"  ; Replace by actual name of table.
      List                   ; This list is one row in the table.
         Concept "thing"     ; Entry in that column, if its a string.
         NumberNode 42       ; If that column type is a number.
         ...
         Concept "stuffs"    ; Last column in the table.

Primary and Foreign Keys

The biggest design question is what to do with primary and foreign keys. The simplest solution is to "do nothing" and just import rows from SQL straight-up. Whatever primary/foreign keys are in the SQL tables, they will also appear in the AtomSpace. They will join automatically, due to fundamental AtomSpace architecture. With this solution, writing complex queries appears to be straight-forward (and easier than writing SQL queries). This works and is surprisingly flexible.

Other mappings are possible; however, there is no natural way of asking Postgres which table columns are foreign keys, and which other tables they might reference. If this info was available, then we could have a an Atomese representation that does NOT keep any keys at all in the AtomSpace, and instead just makes direct links between table rows. So, for example:

   Edge
      Predicate "some join relation"
      Set
         Edge   ;;; row in the host table
            Predicate "some tablename"
            List ...

         Edge   ;; row in the target table.
            Predicate "another tablename"
            List ...

         Edge   ;; if more than two tables are joined.
            Predicate "yet another tablename"
            List ...

See the OpenCog wiki:

• EdgeLink
• PredicateNode

From what I can tell, the above alternate form uses about the same amount of RAM as having explicit keys in each row. It also takes just about the same amount of time to query over. So it does not seem to offer any size or performance advantage over brute-force primary/foreign keys.

It does seem to make things more readable, more "natural" in Atomese. It provides more flexibility: you can create and destroy joins at any time. You can join some rows but not others. All the usual stuff that makes the AtomSpace more flexible than SQL.

For just right now, we punt, and store the naked PRIMARY/FOREIGN KEY values as Atoms in the AtomSpace. It feels ugly, but it works.

Table Schemas

SQL table definitions provide a definition of the columns of that table. These are imported into the AtomSpace, where they are used to find the names of the columns, and the types. (Note that the EdgeLink example above does not contain the column names.) Below is the current mapping.

The SQL column names are recorded as VariableNode names. The type of each variable aka column is given.

    Signature
       Predicate "tablename"    ;; Replace by actual table name.
       List
          TypedVariable
              Variable "name of column 1"
              Type 'ConceptNode ;; For SQL text/varchar
          TypedVariable
              Variable "name of column 2"
              Type 'NumberNode  ;; For SQL numbers
          ...

See the OpenCog wiki:

• SignatureLink
• VariableNode
• TypedVariable
• TypeNode

The base AtomSpace supports only a few primitive types; there's no direct analog to the varied primitive types that SQL has. So far, it doesn't seem to be needed. Perhaps the set of primitive types could be enriched, e.g. by creating:

• StringNode for SQL TEXT and VARCHAR (instead of ConceptNode)
• DateNode for SQL dates and times.
• IntegerNode (the existing NumberNode is a vector of floats. It works great, but some people just love ints.)

Specific databases might benefit from custom types:

• GeneNode
• ProteinNode
• URLNode
• HumanReadableDescriptionNode
• YourFavoriteIdeaHereNode

The agi-bio project provides the first two types. The cheminformatics project provides types for atomic elements and molecular binding.

Using

Below is a sketch of how things could work. For actual examples that actually run and actually work correctly, see the examples directory.

Examples of accessing data in a foreign database.

; Describe where it is located.
(define foreign-db
   (BridgeStorageNode "postgres://example.com/foo?user=foo&passwd=bar"))

; Open it.
(cog-open foreign-db)

; Load the *entire* table `gene.allele`. Optional; only if you
; actually want the whole table in RAM. The table name is known
; in advance, and is given directly.
(fetch-incoming-set (Predicate "gene.allele"))

; Instead of loading entire tables, perhaps we only want all
; rows of all tables that mention gene CG7069.
(fetch-incoming-set (Concept "CG7069"))

; Perhaps we plan to do a join. So, load *all* tables that have
; a given column name. In this case, all tables having a column
; called "genotype".
(fetch-incoming-set (Variable "genotype"))

; StorageNodes do have the ability to run generic queries, and
; we could, in principle, translate at least some of the simpler
; Atomese queries into SQL, and run those.
(fetch-query (Meet (Edge (Predicate "gene.allele")
    (List (Concept "CG7069") (Glob "rest of the row")))))

; The fetch-query function is already built into the base, core
; AtomSpace. We could also create custom functions:
(cog-bridge-get-row "gene.allele" (Concept "CG7069"))

; Custom functions are not appealing, since they don't work
; with the rest of the StorageNode and ProxNode infrastructure.

It could be convenient to introduce special-purpose Atom types, such as GeneNode from the agi-bio project. This would allow queries such as

(fetch-incoming-set (Gene "CG7069"))

which could be marginally more efficient, presuming that the gene.allele table schema was properly declared:

    Signature
       Predicate "gene.allele"
       VariableList
          TypedVariable
              Variable "symbol"
              Type 'GeneNode
          TypedVariable
              Variable "is_alleleof"
              Type 'NumberNode
          TypedVariable
              Variable "propagate_transgenic_uses"
              Type 'NumberNode
          TypedVariable
              Variable "gene_is_regulatory_region"
              Type 'NumberNode
          ...

Building and Installing

This module works. It can load tables, it can load joining columns, and it can join rows, all "automatically". The build process is identical to that of other modules in OpenCog.

Prerequisites

AtomSpace

• The AtomSpace, of course.
• https://github.com/opencog/atomspace
• It uses exactly the same build procedure as this package. Be sure to sudo make install at the end.

Postgres

• SQL Database
• https://postgres.org | apt install postgresql postgresql-client libpq-dev

Building this module

Be sure to install the pre-requisites first! Perform the following steps at the shell prompt:

    cd to project root dir
    mkdir build
    cd build
    cmake ..
    make -j4
    sudo make install
    make -j4 check

Open Questions

Some issues to ponder:

• What's the right solution to the foreign-key dilemma?

• The flybase dataset seems to have a large number of extremely complex SQL stored procedures. What are they? What do they do? What should we do with them?

• What to do with views?

• What if the same table appears in multiple schemas?

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