Rel Data Types

This reference guide describes the various data types in Rel.

Overview

Category		Name	Description
Numeric	Primitive	`SignedInt[8]`, `SignedInt[16]`, `SignedInt[32]`, `SignedInt[64]`, and `SignedInt[128]`	Signed integers.
Numeric	Primitive	`UnsignedInt[8]`, `UnsignedInt[16]`, `UnsignedInt[32]`, `UnsignedInt[64]`, and `UnsignedInt[128]`	Unsigned integers.
Numeric	Primitive	`Floating[16]`, `Floating[32]`, and `Floating[64]`	Floating-point numbers.
Numeric	Primitive	`Rational[8]`, `Rational[16]`, `Rational[32]`, `Rational[64]`, and `Rational[128]`	Rational numbers.
Numeric	Primitive	`FixedDecimal[nbits, ndecimals]`	Fixed-sized decimals with `ndecimals` digits of decimal precision and total bit size of `nbits`.
Numeric	Abstract	`Number`	Union of all numeric data types.
Text	Primitive	`Char`	UTF-16 characters.
Text	Primitive	[`String`]/rel/ref/data-types/text(#string)	Variable-sized strings.
Time	Primitive	`DateTime`	Timestamps containing date and time information.
Time	Primitive	`Date`	Date.
Time	Primitive	`Year` , `Month` , `Week`, and `Day`	Date periods.
Time	Primitive	`Hour`, `Minute`, `Second`, `Millisecond`, `Microsecond`, and `Nanosecond`	Time periods.
Key	Primitive	`Hash`	Hash value.
Key	Primitive	`AutoNumber`	Integer autonumbers.
Key	Abstract	`Entity`	Entity key, union of `Hash` and `AutoNumber`.
Meta	Primitive	`RelName`	Symbols. Can be used to specify names of relations.
Other	Abstract	`Any`	Union of all data types.
Other	Primitive	`boolean_true` and `boolean_false`	Boolean data type (for JSON support only).
Other	Primitive	`FilePos`	File positions in a data file.
Other	Primitive	`Missing`	Singleton representing missing data.

Rel classifies data types based on their main purpose:

Category	Description
Numeric	Numeric data types.
Text	Text-based data types.
Time	Time-related data types.
Key	Data types for identification purposes, such as UUIDs.
Meta	Data types referring to metadata information (such as relation names).
Other	All other supported data types.

Rel also distinguishes between two kinds of data types:

	Description
Primitive	Data types with no further subtypes.
Abstract	Data types built on top of primitive types, usually unions of multiple primitive data types.

Introduction

Relations are unordered collections of tuples. A tuple is an ordered collection of individual data values. Each data value has a data type.

In Rel, each data type has an associated unary relation, which includes all the values of that type. Type relations are often infinite, and therefore cannot be listed directly, but are still useful when specifying knowledge graphs, data schemas, and constraints.

Checking types is particularly useful for integrity constraints, as many of the examples in this document show. See Integrity Constraints for more details.

For each data type, Rel generally provides:

A way to construct values of that data type.
A type relation that tests if a given value belongs to that type.
Operations specific to the data type.

The following sections describe each supported data type and provide examples of how they can be used:

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