Relations & Directives

Relations are the core data structures in FlowLog. Every relation is declared with .decl and annotated with I/O directives that determine whether it holds input data or computed results.

Declaring relations

Use .decl to define a relation's schema. Each column has a name and a data type:

.decl Edge(src: int32, dst: int32)
.decl Person(id: int64, name: string, active: bool)

EDB vs IDB relations

FlowLog distinguishes two kinds of relations:

• EDB (Extensional Database) — input relations whose data comes from external files. Marked with .input.
• IDB (Intensional Database) — computed relations whose contents are derived by rules. Marked with .output or .printsize.

A relation cannot be both EDB and IDB. If a relation has an .input directive, it cannot also have .output or .printsize, and vice versa.

.input directive

The .input directive tells the compiler how to read data for an EDB relation:

.decl Arc(x: int32, y: int32)
.input Arc(IO="file", filename="Arc.csv", delimiter=",")

Parameters:

Parameter	Description	Example
IO	I/O method (currently "file")	IO="file"
filename	Path to the input CSV file	filename="Arc.csv"
delimiter	Column separator	delimiter=","

When running the compiler with -F <DIR>, the filename is resolved relative to that directory.

.output directive

The .output directive marks an IDB relation for result output:

.decl Reach(id: int32)
.output Reach

Pass -D <DIR> to the compiler to write output CSVs to a directory, or -D - to print tuples to stderr.

.printsize directive

The .printsize directive prints the cardinality (number of tuples) of a relation after execution:

.decl Reach(id: int32)
.printsize Reach

A relation can have both .output and .printsize.

Complete example

// EDB relations — loaded from CSV files
.decl Source(id: int32)
.input Source(IO="file", filename="Source.csv", delimiter=",")

.decl Arc(x: int32, y: int32)
.input Arc(IO="file", filename="Arc.csv", delimiter=",")

// IDB relation — computed by rules
.decl Reach(id: int32)
.printsize Reach

Reach(y) :- Source(y).
Reach(y) :- Reach(x), Arc(x, y).

Validation

FlowLog validates declarations at parse time:

• Duplicate .input, .output, or .printsize directives for the same relation are rejected.
• A directive that references an undeclared relation causes a parse error.
• A relation with both .input and .output (or .printsize) is rejected.