Data

Example data

Here we'll build the following relvars which we'll use throughout the documentation: 

S := {SNO:str,  SNAME:str,  STATUS:int,  CITY:str}{
     ["S1",     "Smith",    20,          "London"]
     ["S2",     "Jones",    10,          "Paris"]
     ["S3",     "Blake",    30,          "Paris"]
     ["S4",     "Clark",    20,          "London"]
     ["S5",     "Adams",    30,          "Athens"]
}

P := {PNO:str, PNAME:str, COLOR:str, WEIGHT:int, CITY:str}{
     ["P1",    "Nut",     "Red",     12,         "London"]
     ["P2",    "Bolt",    "Green",   17,         "Paris"]
     ["P3",    "Screw",   "Blue",    17,         "Rome"]
     ["P4",    "Screw",   "Red",     14,         "London"]
     ["P5",    "Cam",     "Blue",    12,         "Paris"]
     ["P6",    "Cog",     "Red",     19,         "London"]
}

SP := {SNO:str, PNO:str, QTY:int}{
      ["S1",    "P1",    300]
      ["S1",    "P2",    200]
      ["S1",    "P3",    400]
      ["S1",    "P4",    200]
      ["S1",    "P5",    100]
      ["S1",    "P6",    100]
      ["S2",    "P1",    300]
      ["S2",    "P2",    400]
      ["S3",    "P2",    200]
      ["S4",    "P2",    200]
      ["S4",    "P4",    300]
      ["S4",    "P5",    400]
}

We can add some integrity constraints to ensure our data remains valid. We'll go over these in a later section. 

Constraint := {name:str,             rule:str}{
              ["Constraint_key",     "key(Constraint, {name})"],
              ["S_key",              "key(S, {SNO})"],
              ["P_key",              "key(P, {PNO})"],
              ["SP_key",             "key(SP, {SNO,PNO})"],
              ["S_SP_FK",            "SP{SNO} ⊆ S{SNO}"],
              ["P_SP_FK",            "SP{PNO} ⊆ P{PNO}"],
}

Later, we'll also add views (derived relvars).

Here are some more things to note about variables in Ra:

We can display the relvar values, in this case as HTML tables, but note that the left-to-right ordering is arbitrary as is the top-to-bottom order of the tuples. We'll introduce operators to specify both of these orderings later, purely for output purposes, because after that point we'll no longer be dealing with relations. Again, relations have no attribute or tuple order to them. 

S
SNOSNAMESTATUSCITY


S1Smith20London


S2Jones10Paris


S3Blake30Paris


S4Clark20London


S5Adams30Athens


P
PNOPNAMECOLORWEIGHTCITY


P1NutRed12London


P2BoltGreen17Paris


P3ScrewBlue17Rome


P4ScrewRed14London


P5CamBlue12Paris


P6CogRed19London


SP
SNOPNOQTY


S1P1300


S1P2200


S1P3400


S1P4200


S1P5100


S1P6100


S2P1300


S2P2400


S3P2200


S4P2200


S4P4300


S4P5400


Constraint
namerule


Constraint_keykey(Constraint, {name})


P_SP_FKSP{PNO} ⊆ P{PNO}


P_keykey(P, {PNO})


SP_keykey(SP, {SNO,PNO})


S_SP_FKSP{SNO} ⊆ S{SNO}


S_keykey(S, {SNO})

Storage details

Ra persists global relvars to disk files, currently as <table>s in HTML files in the schema directory (the one Ra was started in). Although storing data in HTML files has some space overheads, there are some benefits to using HTML: