Description
For this project you will
be writing Datalog queries and will be developing a non-recursive Datalog interpreter. The EBNF
rules that will be used for the dialect of Datalog are in the following section. For this project
Datalog queries will be constructed of a set of rules that will each have a rule head. Each rule head
specifies the rule name and a set of variables. Each rule that does not have a rule body is considered
a fact (also known as external rule); these facts will be backed by CSV data files that have the
tuples that specify when the rule is true. Any other tuples do not satisfy the fact rules. Rules that
have a rule body are to be calculated and attempt to find the values that will satisfy all of the
subgoals. If multiple rules exist with the same name, then rule invocations of that name are
considered to be a union of the multiple rules. The goal of the Datalog interpreter is to find all
tuples that satisfy all of the rules specified, with the base values coming from the fact rules.
Non-Recursive Datalog Programming Language
The following EBNF describes the non-recursive Datalog language. The Non-terminals on the
right are identified by italics. Literal values are specified in bold. The operators not in bold or
italics describe the options of the EBNF. These operators are {} for repetition, [] for optional, ()
for grouping, and | for or.
EBNF Rules:
Query := Rule { Rule }
Rule := [ RuleHead [ := RuleBody ] ] NewLine
RuleHead := RuleName ( HeadVariableList )
RuleBody := SubGoal { AND SubGoal }
RuleName := Identifier
HeadVariableList := Identifier { , Identifier }
SubGoal := RuleInvocation | NegatedRuleInvocation | EqualityRelation
RuleInvocation := RuleName ( BodyVariableList )
NegatedRuleInvocation := NOT RuleInvocation
EqualityRelation := InequalityRelation { EQOperator InequalityRelation }
BodyVariableList := InvocationVariable { , InvocationVariable }
InequalityRelation := Term { IEQOperator Term }
EQOperator := != | =
InvocationVariable := Identifier | EmptyIdentifier
Term := SimpleTerm { AddOperator SimpleTerm }
IEQOperator := < | > | <= | >=
SimpleTerm := UnaryExpression { MultOperator UnaryExpression }
AddOperator := + | –
UnaryExpression := ( UnaryOperator UnaryExpression ) | PrimaryExpression
MultOperator := * | / | %
UnaryOperator := ! | – | +
PrimaryExpression:= ( EqualityRelation ) | Constant | Identifier
Constant := IntConstant | FloatConstant | StringConstant
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Token Rules:
Identifier := Alpha { ( Digit | Alpha ) }
EmptyIdentifier := _
IntConstant := Digit { Digit }
FloatConstant := Digit { Digit } [ . Digit { Digit } ]
StringConstant := ” { ( CharacterLiteral | EscapedCharacter ) } ”
Comment := # { ( WhiteSpace | Printable ) } NewLine
Digit := 0 – 9
Alpha := A – Z | a – z
WhiteSpace := Tab | CarriageReturn | \ NewLine | Space
Printable := Space – ~
CharacterLiteral := Space – ! | # – [ | ] – ~
EscapedCharacter := \b | \n | \r | \t | \\ | \’ | \”
Semantics:
There are several requirements for the non-recursive Datalog queries that cannot be expressed in
the EBNF. The following must be true of all valid queries:
• All subgoals must be defined prior to their use
• All repeated rule names must be defined contiguously
• All repeated rule names must have the same number of variables
• Any variable in the rule head or rule body must appear in a non-negated rule invocation
• A rule invocation may not appear in its own rule definition (i.e. recursive definition)
• Fact rules may only appear once
• Every rule invocation must provide the same number of variables as its definition
CSV Data Files
The facts can be stored in a CSV files. The name of the file without .csv extension will be the name
of the facts loaded into the environment. Each column is a different attribute, with the header row
containing the attribute name. Four data types are allowed in the CSV files: string, float, integer,
and boolean. Rows two and on, each have one tuple in them.
The following is an example of fact R that would be in the file R.csv:
“a” “b” “c” “d”
3 “Hello” 3.4 true
4 “World” 1.1 false
6 “Goodbye” 8.8 false
7 “None” 9.3 true
Datalog Examples
The following are a few Datalog query examples using the grammar described in the previous
sections using the R fact described.
Simple fact query:
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R(a,b,c,d)
This will result in the following output:
a b c d
3 Hello 3.4 true
4 World 1.1 false
6 Goodbye 8.8 false
7 None 9.3 true
Simple filtering for a being greater than 5:
R(a,b,c,d)
S(x) := R(x,_,_,_) AND x > 5
This will result in the following output:
x
6
7
Simple filtering for c being greater than 8.0 or less than 3.0:
R(a,b,c,d)
S(x) := R(_,_,x,_) AND x > 8.0
S(x) := R(_,_,x,_) AND x < 3.0
This will result in the following output:
x
1.1
8.8
9.3
Find all b associated with c not being the smallest in R:
R(a,b,c,d)
S(x) := R(_,x,c1,_) AND R(_,_,c2,_) AND c1 > c2
This will result in the following output:
x
Hello
Goodbye
None
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Datalog Queries
Write Datalog queries for the questions posed below. Name your query files query_X.nrdl
where X is the number of the question below. You may assume the following facts will be
available:
Product(maker, model, year)
Car(model, city, highway, style, passengers, trunk, msrp)
Pickup(model, city, highway, passengers, cargo, towing, msrp)
EV(model, range, battery, passengers, msrp)
1) What Car models have a highway less than 35miles? The final rule head should be
Answer(model).
2) Find all of the Pickup models that have a cargo capacity of at least 75cu ft. and a highway
fuel economy less than 25MPG. The final rule head should be Answer(model).
3) Find all automakers that sell at least one vehicle that msrp less than $27,000 and at least
one vehicle greater than $55,000. The final rule head should be Answer(maker).
4) Find the passenger capacities that exist for three or more vehicles. That is three or more
different vehicles should have that passenger capacity. The final rule head should be
Answer(passengers).
5) Find the automaker(s) of the highest combined fuel economy (55% city, 45% highway)
of conventional vehicles (cars and pickups). The final rule head should be
Answer(maker).
6) Find the vehicle model with the highest miles per gallon gasoline equivalent (MPGGE).
For this problem assume combined fuel economy formula from above, and that a gallon
of gasoline is equivalent to 33.1kWh. The final rule head should be Answer(model).
7) Find automaker(s) that sell a pickup with a highway fuel economy lower than all the cars
it sells. The final rule head should be Answer(maker).
Datalog Interpreter
The Datalog interpreter will be constructed from several classes. A given NRDatalog class
provides a class that can parse command line arguments and instantiate and call the appropriate
classes. The following classes should be created with at least the specified interface.
// Class that parses the non-recursive Datalog language
public class NRDatalogParser{
// Constructor for the parser
public NRDatalogParser(PeekableCharacterStream stream);
// Parses a query and returns true if valid query
public boolean parseQuery();
// Prints out the error if one has occurred
public void printError(PrintStream ostream);
}
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// Class that will construct the parse tree from
public class NRDatalogParseTree extends NRDatalogParser{
// Constructor for the parse tree
public NRDatalogParseTree(PeekableCharacterStream stream);
// Parses a query and returns true if valid query
public boolean parseQuery();
// Prints out the error if one has occurred
public void printError(PrintStream ostream);
// Outputs a tree of the parsed query
public void outputParseTree(PrintStream ostream);
}
// Class that will construct and execution tree from the parse
// tree. Executes the query and displays the results.
public class NRDatalogExecutionTree extends NRDatalogParseTree{
// Constructor for the execution tree
public NRDatalogExecutionTree(PeekableCharacterStream stream);
// Parses a query and returns true if valid query
public boolean parseQuery();
// Prints out the error if one has occurred
public void printError(PrintStream ostream);
// Outputs a tree of how execution would occur for queries
public void outputExecutionTree(PrintStream ostream);
// Sets the verbosity setting for execution
public void setVerbose(boolean verb);
// Sets the number of threads during execution
public void setThreadCount(int threadcount);
// Sets the path to the data files
public void setDataPath(String datapath);
// Executes the parsed query
public boolean executeQuery();
}
Suggested Approach
1. Work on writing the Datalog queries first. An example program is available to execute the
queries. This will provide you the basic understanding of how the operations should work
from the query writing perspective.
2. Update your Scanner to accommodate the new set of operators. Make sure to change the
newline to an operator, if a whitespace newline is desired, it must be preceded with a
backslash. There are only two keywords AND and NOT.
3. Write the NRDatalogParser class to recognize the non-recursive Datalog language. Similar
to project 2 you will want one method per rule. Creating an enum class that represents each
rule and creating an isFirst method may aid in the development of the rules.
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4. Write the NRDatalogParseTree class to construct the parsed query as a tree. You will likely
want to create some type of node class within the NRDatalogParseTree that holds the rule
type, associated token (if any), parent, and children. You may find using a stack data
member will be helpful in the recursive decent parsing. The top of the stack can hold the
current parent node.
5. Write a class to hold the data sets. These should be able to hold a set of list of objects. Each
list of objects can act as data tuple. It should also have a list of column names. This class
should be able to be constructed from a PeekableCharacterStream (so to load using CSV),
or from list of column names and the set of list of objects. The data set class should support:
a. Appending tuples at least privately (this will help constructing new data sets)
b. Filtering (or selecting) tuples given an object that has function returning if the tuple
should be in the new data set or not (this will essentially remove rows from the data
set)
c. Projecting specified columns to a new data set (this is similar to cutting off columns
that are not desired, may want to consider supporting renaming of the columns with
this as well)
d. Cartesian product with another data set to create a new data set
e. Natural join with another data set to create new data set
f. Filter (or selecting) tuples given tuples do not appear in another data set (the tuple
should be kept if the combination of columns specified do not appear in the other
data set.
g. Union with another data set to create a new data set (it is assumed that both have
the same column names)
h. Reordering columns to create a new data set (may be helpful when projecting down
temporary work into final rule)
6. Write the NRDatlogExecutionTree class to construct the tree to that it can easily be
executed. You will likely want to create some type of node class within the
NRDatlogExecutionTree that holds the rule type, associated token (if any), parent,
children, and possibly a node index (may be helpful for sorting step).
a. Translate the parse tree into an execution tree. The difference is that infix operators
will be migrated up to be the parent of the operands instead of being children of the
larger rule. You will likely want to write a function that recursively visits the nodes
of the parse tree and returns a converted execution tree node equivalent. Tokens
like open/close paren, assignment, and commas should be omitted. The body sub
goals should also be sorted for simplicity of execution. Rule invocations should be
first, followed by negated rule invocations and finally equality relations.
b. Write a method to validate the semantic rules for the execution tree. This will make
sure that execution should be able to proceed.
c. Write a method to execute a rule without a rule body. This will essentially just load
a data set and add it to the calculated rules.
d. Write a method to execute a rule with a rule body. This will create a temporary
calculated data set that will either be added to the calculated rules or unioned with
the previously calculated rule of the same name.
i. Create the ability to invoke rules by projecting them based upon the
invocation. This projected invocation will then be either naturally joined or
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cartesian product with the temporary calculated data set depending if there
are any overlap in column names.
ii. Create the ability to do a negated invocation, this is similar to invoking
rules; however, this will potentially be removing tuples from the temporary
data set instead of adding tuples.
iii. Create the ability to filter the tuples based upon the equality relations. A
filter object should be created using the subgoal and should be able to
calculate if a tuple should be kept or omitted.
Examples of valid and invalid nrdl files are in /home/cjnitta/ecs140a/proj4 on the
CSIF. Script that runs the NRDatalog class can be found there too. Runnig the script without
options, or with the –help option will print the help. Your code will be tested on the CSIF and
is expected to compile and run on the CSIF.
You must submit the source file(s), a Makefile, and README.txt file, in a tgz archive. Do a
make clean prior to zipping up your files so the size will be smaller. You will want to be in the
parent directory of the project directory when creating the tgz archive. You can tar gzip a directory
with the command:
tar -zcvf archive-name.tgz directory-name
You should avoid using existing source code as a primer that is currently available on the Internet.
You must specify in your readme file any sources of code that you have viewed to help you
complete this project. You must also provide the URL any code sources in comments of your
source code. All class projects will be submitted to MOSS to determine if students have
excessively collaborated. Excessive collaboration, or failure to list external code sources will result
in the matter being referred to Student Judicial Affairs.
Helpful Hints
• The use of peekNextToken()will be helpful in some instances where it isn’t clear what
the next rule should be parsed. The language is designed so that only a single look ahead
is necessary.
• Creating an enum class for the rule names will be helpful in multiple levels and is highly
encouraged.
• Use the working example to output the parse tree and the execution tree. Being able to
match them will help prior to executing the queries.
• Using Integer, Float, String, and Boolean types will allow the data sets to hold lists of
Objects. The instanceof operator will be helpful in detecting the type during calculations
of evaluations.
Extra Credit
After successfully creating a Datalog interpreter convert the NRDatalogExecutionTree into a
multithreaded version. The executeQuery method needs to use multiple threads to execute the
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query in parallel on systems with multiple cores. Larger data sets with a query that requires
significant time will be provided later.
