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(** Relation: a lightweight versioned root describing a named collection of
tuples. Physical storage owns the tuple B+ tree; this object holds only
metadata and a tree pointer.
Class hierarchy:
- [relation] — base, storable, has membership_criteria/provenance/lineage
- [ephemeral_relation] — adds a generator (query-time computed, not stored)
- [pseudo_relation] — adds a producer (system-defined, not stored)
- [domain] — adds a generator (system or user defined, not necessarily
stored) *)
module RelationConstraint = struct
type name = string
type t = (name * Constraint.t) list
end
module Lineage = struct
(** Tracks which relational algebra operations produced the tuples. Lives in
the relation, but refers to the tuple. *)
type t =
| Base of Conventions.Name.t
| Select of t
| Project of Conventions.Name.t list * t
| Join of t * t
| ThetaJoin of t * t
| Sort of t
| Take of t
end
module Provenance = struct
type source = { relation : Conventions.Name.t; attribute : string }
(** Tracks which base relation each attribute originates from. Lives on the
relation and refers to the `entity group`. *)
type t =
| Undefined
| Base of Conventions.Name.t
| Sources of source list BatMap.String.t
(** Maps attribute name -> list of sources (multiple after joins) *)
let base ~relation ~attributes : t =
Sources
(List.fold_left
(fun acc attr ->
BatMap.String.add attr [ { relation; attribute = attr } ] acc)
BatMap.String.empty attributes)
let empty : t = Sources BatMap.String.empty
let undefined : t = Undefined
end
type producer = (string * Conventions.AbstractValue.t) list -> Generator.t
type kind = [ `Stored | `Ephemeral | `Pseudo | `Domain ]
class virtual relation = object (_self)
method virtual kind : kind
method virtual name : Conventions.Name.t
method virtual schema : Schema.t
method virtual hash : Conventions.Hash.t
method virtual constraints : RelationConstraint.t option
method virtual cardinality : Conventions.Cardinality.t
method virtual lineage : Lineage.t
method virtual provenance : Provenance.t
method virtual membership_criteria : Tuple.t -> bool
method virtual timestamp : float
method virtual serialize : unit -> Storable.Relation.t
end
class stored
~name:(init_name : Conventions.Name.t)
~schema:(init_schema : Schema.t)
~constraints:(init_constraints : RelationConstraint.t option)
~cardinality:(init_cardinality : Conventions.Cardinality.t)
~membership_criteria:(init_membership : Tuple.t -> bool)
~lineage:(init_lineage : Lineage.t option)
~provenance:(init_provenance : Provenance.t option) =
let init_hash =
Conventions.Hash.hash_text (init_name ^ Schema.to_string init_schema)
in
object (self)
inherit relation
val name = init_name
val hash = init_hash
val schema = init_schema
val tree_pointer : Conventions.Hash.t option = None
val constraints = init_constraints
val cardinality = init_cardinality
val membership_criteria = init_membership
val timestamp = Unix.gettimeofday ()
val lineage = Option.value init_lineage ~default:(Lineage.Base init_name)
val provenance = Option.value init_provenance
~default:(Provenance.base ~relation:init_name ~attributes:(Schema.attributes init_schema))
method name = name
method kind = `Stored
method hash = hash
method schema = schema
method tree_pointer = tree_pointer
method constraints = constraints
method cardinality = cardinality
method membership_criteria = membership_criteria
method timestamp = timestamp
method lineage = lineage
method provenance = provenance
method private compute_hash tp =
let tree_hash = match tp with Some h -> h | None -> "" in
Conventions.Hash.hash_text (name ^ Schema.to_string schema ^ tree_hash)
method private advance tp =
{< hash = self#compute_hash tp;
tree_pointer = tp;
timestamp = Unix.gettimeofday () >}
method set_tree_pointer tp = self#advance tp
method set_cardinality c = {< cardinality = c >}
method set_constraints c = {< constraints = c >}
method serialize () = { Storable.Relation.name = name; schema }
end
class ephemeral
~name:(init_name : Conventions.Name.t)
~schema
~constraints
~cardinality ~membership_criteria
~lineage
~provenance
~generator:(init_generator : Generator.t) =
object
inherit relation
val name : Conventions.Name.t = init_name
val schema : Schema.t = schema
val generator : Generator.t = init_generator
val constraints = constraints
val cardinality = cardinality
val membership_criteria = membership_criteria
val lineage = Option.value lineage ~default:(Lineage.Base init_name)
val provenance = Option.value provenance ~default:(Provenance.Base init_name)
val timestamp = Unix.gettimeofday ()
method name = name
method kind = `Ephemeral
method schema = schema
method generator = generator
method hash = Conventions.Hash.hash_text (name ^ "ephemeral")
method constraints = constraints
method cardinality = cardinality
method membership_criteria = membership_criteria
method lineage = lineage
method provenance = provenance
method timestamp = timestamp
method serialize () = failwith "Ephemeral relations cannot be serialized directly"
end
class pseudo
~name:(init_name : Conventions.Name.t) ~schema ~constraints ~cardinality ~membership_criteria ~lineage ~provenance
~producer:(init_producer : producer) =
object
inherit relation
val name = init_name
val schema = schema
val producer = init_producer
val constraints = constraints
val cardinality = cardinality
val membership_criteria = membership_criteria
val lineage = Option.value lineage ~default:(Lineage.Base init_name)
val provenance = provenance
val timestamp = Unix.gettimeofday ()
method name = name
method kind = `Pseudo
method schema = schema
method producer = producer
method as_generator (bindings : (string * Conventions.AbstractValue.t) list) : Generator.t = producer bindings
method hash = Conventions.Hash.hash_text (name ^ "pseudo")
method constraints = constraints
method cardinality = cardinality
method membership_criteria = membership_criteria
method lineage = lineage
method provenance = provenance
method timestamp = timestamp
(* TODO: Remove this from the virtual definition *)
method serialize () = failwith "Pseudo relations are procedural"
end
let deserialize_stored (_bytes : bytes) : (stored, string) result =
try
let stored = Storable.Relation.of_bytes _bytes in
let membership_criteria =
Constraint.build_membership_criteria ~_name:stored.name ~schema:stored.schema
in
Ok
(new stored ~name:stored.name ~schema:stored.schema ~constraints:None
~cardinality:Conventions.Cardinality.ConstrainedFinite
~membership_criteria ~lineage:None ~provenance:None)
with Invalid_argument message -> Error message
class domain ~name ~schema ~constraints ~cardinality ~membership_criteria
~lineage ~provenance ~generator =
object
inherit ephemeral
~name ~schema ~constraints ~cardinality
~membership_criteria ~lineage
~provenance ~generator
method! kind = `Domain
end
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