Using Rel359
The main window of Rel359 contains two main panes.
Simply type M359 Language statements into the bottom pane, click the Run button
(or press F5) and the results are shown in the upper pane.
One of the design goals of Rel359 was to support all M359 Language statements
exactly as described in the course text. This was almost achieved and any
differences are listed below. (See Limitations for
more infomation about these differences.)
-
Rel359 does not support domains, it only
supports simple types of CHAR, INTEGER & RATIONAL. If you have installed
the Java SDK then you should be able create additional custom types but this
has not been tested in Rel359 and is not documented on this site.
-
Rel359 does not support dates. Dates are treated as strings and therefore
don't sort or compare properly unless entered using a format such at
ISO 8601 (YYYY-MM-DD).
-
Rel359 does not support foreign keys.
-
Rel359 only supports a limited number of M359 style constraints.
(Currently upto 1000 M359 style constraints are supported.)
-
Rel359 does not support comments when defining relations.
-
Rel359 requires imperative statements to be terminated with a semicolon.
M359 Language Examples
The following table lists examples of M359 Language statements and how they can be used in Rel359.
|
operator
|
example
|
comment
|
|
select
|
select Enrolment where CourseCode = 'c4'
|
as in the course text
|
|
project
|
project Enrolment over StudentId, CourseCode
|
as in the course text
|
|
join
|
Enrolment join Student
|
as in the course text
|
|
rename |
Student join (Region rename
(Address as RegionAddress, EmailAddress as RegionEmailAddress))
|
as in the course text
|
|
alias
|
ExamAndEnrolDetails alias (Enrolment join Examination);
|
requires a semicolon at the end
|
|
divide
|
divide SupplyParts by AllParts
|
as in the course text
|
|
intersection
|
(project Student over Name, Address) intersection (project Staff
over Name, Address)
|
as in the course text
|
|
union
|
BasicStudent union NewStudent
|
as in the course text
|
|
difference
|
BasicStudent difference ExStudent
|
as in the course text
|
|
times
|
project (select (Enrolment times ( Student rename (StudentId as StudentIdent)))
where StudentId = StudentIdent) over StudentId, CourseCode, EnrolmentDate, Name, Address, EmailAddress, RegistrationDate, RegionNumber
|
as in the course text
|
|
constraint
|
constraint (select (Enrolment join Student) where EnrolmentDate < RegistrationDate)
is empty;
|
requires a semicolon at the end
a maximum of 1000 constraints are supported
|
|
relation
|
relation OwnsHouse
Address: CHAR
Ref: CHAR
WhenLastSold: INTEGER
primary key (Address, Ref);
|
requires a semicolon at the end
composite keys are supported
|
primary key
alternate key
|
relation OwnsHouse
Address: CHAR
Ref: CHAR
primary key Address
alternate key Ref;
|
requires a semicolon at the end
multiple alternate keys are supported
comments are not supported
foreign keys are not supported
|
Notes
Case sensitivity - Rel359 requires all names (of relations, attributes, etc.) to be spelled exactly as defined. However, it is case-insensitive with respect to key words like
join and
where.
Rel359 System Relations
In addition to any relations created by the user, Rel359 contains a number of system relations
which contain information about Rel359 and metadata about all the other relations. These relations
should support all the relational operators mentioned above but you should
not attempt to modify these relations directly. However several of these relations contain
information that is useful to the user.
-
sys.Catalog - contains details of all other relations, both system and user.
Select from this relation to find all the relations that you have defined.
-
sys.Constraints - contains details of all the constraints defined in the database.
If you wish to delete a constraint, you will need to select from this to find its name.
-
sys.Version - contains version, license and copyright information about Rel359.
Non M359 Language Operators
The M359 Language is incomplete in that it does not contain any operators for inserting, updating or
deleting data in relvars. It also contains no operators for deleting relations, constraints, etc.
Since Rel359 is based on Rel it inherits Tutorial D style operators for features that are not
in the M359 Language.
Populating Relations
Relations can be populated with single tuples....
Ward := RELATION { TUPLE {WardNo "w10" , WardName "Arden" , NumberOfBeds 12 }};
....or by multiples
Ward := RELATION {
TUPLE {WardNo "w11" , WardName "Feldon" , NumberOfBeds 12 },
TUPLE {WardNo "w12" , WardName "Avon" , NumberOfBeds 8 },
TUPLE {WardNo "w13" , WardName "Mendip" , NumberOfBeds 10 }};
This syntax overwrites any existing tuples in the relation.
Insert
Tuples can be inserted singly....
INSERT Ward RELATION { TUPLE {WardNo "w10" , WardName "Arden" , NumberOfBeds 12 }};
....or in multiples
INSERT Ward RELATION {
TUPLE {WardNo "w11" , WardName "Feldon" , NumberOfBeds 12 },
TUPLE {WardNo "w12" , WardName "Avon" , NumberOfBeds 8 },
TUPLE {WardNo "w13" , WardName "Mendip" , NumberOfBeds 10 }};
Delete
Tuples can be deleted selectively....
DELETE Ward WHERE WardNo = "w11";
....or all the tuples in a relation
DELETE Ward;
Note that after running the last line of code above, the Ward relation will be empty but it will still exist.
To delete the entire relation use
DROP Ward;
When specifing data in relations or comparisions CHAR types must be enclosed in 'single quotes'
or "double quotes"; INTEGER and RATIONAL types must not have quotes and RATIONAL types must contain
a decimal point.
When adding, deleting or modifying any data, constraints must be respected otherwise an error
will be thrown.
When attempting to delete relations, the delete will fail if anything depends on the relation.
In particular constraints and aliases depend on other relation and these constraints or
aliases must be deleted first.
Constraints
In the M359 Language constraints are defined in the context of a relation and are not named.
However constraints need to be named so that they can be identified if you want to delete
them later. Rel359 therefore automatically selects a name when you create a constraint
using the M359 Language syntax.
For example if you create a constraint such as
constraint (select (Enrolment join Student) where EnrolmentDate < RegistrationDate) is empty;
You can find its name by running select sys.Constriants
and in this case you can see the constraint is named c5.
Having found the name, you can delete the constraint as follows:
DROP constraint c5;
If you want to control the name of a constraint yourself, Rel359 also supports naming
of contraints when you create them. This is acheived by including the name after the
constraint keyword. For example:
constraint MyConstraint (select (Enrolment join Student) where EnrolmentDate < RegistrationDate) is empty;
Note that using named constraints such as this is outside the M359 Langauge and should not
be used in any assignments.
Foreign keys
Rel359 does not support M359 Language style foreign keys, but you can use contraints to do the
same job. For example the foreign key in the realtion definition for Student:
foreign key RegionNumber references Region
can be implemented using
constraint ((project Student over RegionNumber) difference (project Region over RegionNumber)) is empty;
Note that this syntax includes the attribute being referred to which is missing in the
definition of the M359 Language.