Relations

Here is a relation literal. It has two parts, each between braces. It has a heading and a body.

{     day_seq:int, day_name:str}{
tuple{day_seq:=1,  day_name:="Monday"},
tuple{day_seq:=2,  day_name:="Tuesday"},
tuple{day_seq:=3,  day_name:="Wednesday"},
tuple{day_seq:=4,  day_name:="Thursday"},
tuple{day_seq:=5,  day_name:="Friday"},
tuple{day_seq:=6,  day_name:="Saturday"},
tuple{day_seq:=7,  day_name:="Sunday"},
}

One view of that relation as a table is:

┌─────────┬───────────┐
│ day_seq │ day_name  │
├─────────┼───────────┤
│       1 │ Monday    │
│       2 │ Tuesday   │
│       3 │ Wednesday │
│       4 │ Thursday  │
│       5 │ Friday    │
│       6 │ Saturday  │
│       7 │ Sunday    │
└─────────┴───────────┘

Heading

The heading is a set of attributes: day_seq and day_name in the example above. Each attribute has a name and a type. Currently available types include:

• bool (Boolean: true or false)
• int (64 bit integer)
• float (64 bit floating-point number)
• str(string)
• time(date and/or time)
• tuple{...}(nested tuple)
• {...} (nested relation)

Other types will be discussed or added later.

Body

The body is a set of tuples. A tuple is a set of attribute names and typed values.

For example:

tuple{day_seq:=1, day_name:="Monday"}

Here, the tuple has two attributes: day_seq is assigned the value 1 and day_name is assigned the string "Monday".

Shorthand Syntax for Body Tuples

For convenience, a shorthand syntax allows for specifying the body of the relation using lists of values. This shorthand relies on the left-to-right ordering of the values aligning with the left-to-right ordering of the attributes in the heading.

Here’s the same relation using the shorthand notation:

{day_seq:int, day_name:str}{
          [1, "Monday"],
          [2, "Tuesday"],
          [3, "Wednesday"],
          [4, "Thursday"],
          [5, "Friday"],
          [6, "Saturday"],
          [7, "Sunday"],
}

dee and dum

There are two pre-defined relations named dee and dum which are the ones with no attributes: dee has one tuple, dum has none.

dee

┌┐
││
├┤
││
└┘

dum

┌┐
││
├┤
└┘

Later we'll see how we can use dee in another shorthand to construct single-tuple relations.