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cs-236:relational-database [2017/10/25 23:52]
jrtyler [FAQ]
cs-236:relational-database [2018/10/18 21:53] (current)
pdiddy [Part 2: RDBMS-based Interpreter]
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 Create a relation object that includes methods implementing select, project, and rename operations. The relation and its methods must follow the mathematical definitions described in class and in the textbook. For example, the operators must not produce relations which have duplicate tuples or duplicate names in the schema. Create a relation object that includes methods implementing select, project, and rename operations. The relation and its methods must follow the mathematical definitions described in class and in the textbook. For example, the operators must not produce relations which have duplicate tuples or duplicate names in the schema.
  
-Implement at least 10 tests to validate the select, project, and rename methodsAt least 4 of the 10 tests must mimic a datalog query in that they use a sequence of select, project, and rename to answer the query (in that order). The tests must be documented and justified: what does the test accomplish? Each test must be marked with comments explaining what operation is being performed and why. For the 4 tests that mimic a query, the comments must include the actual query that is being mimicked. Each of the tests must test something different; if one test case tests the same thing as another, it isn't telling you anything new, and therefore it won't be counted as one of the 10 tests.+Implement at least 10 tests to validate the select, project, and rename methods
 +At least 4 of the 10 tests must mimic a datalog query in that they use a sequence of select, project, and rename to answer the query (as explained below in the FAQ). 
 +* The tests must be testing either a select, project, rename, or a query; they may '''​not'''​ test if the relation you create is structured properly (i.e. proper sorting, no duplicates, etc.; while these things are important, they are not what should be tested). 
 +** Both types of selects must be implemented. 
 +The tests must be documented and justified: what does the test accomplish? 
 +** Each test must be marked with comments explaining what operation is being performed and why. 
 +** For the 4 tests that mimic a query, the comments must include the '''​actual query''' ​that is being mimicked. 
 +*Each of the tests must test something different; if one test case tests the same thing as another, it isn't telling you anything new, and therefore it won't be counted as one of the 10 tests.
  
 Further, all the tests must be automatic; '''​automatic means the tests run without any user input and reports to the console the status of every test: pass or fail.'''​ Further, all the tests must be automatic; '''​automatic means the tests run without any user input and reports to the console the status of every test: pass or fail.'''​
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 * '''​Output''':​ see the [[datalog-parser#​Output Specifications|output specifications]] and [[datalog-parser#​Examples | examples]] * '''​Output''':​ see the [[datalog-parser#​Output Specifications|output specifications]] and [[datalog-parser#​Examples | examples]]
  
-Part 2 is scored on a set of 10 private tests at submission. ​+Part 2 is scored on a set of private tests at submission. ​
 ==Examples== ==Examples==
  
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 dc(X,Y)? Yes(1) dc(X,Y)? Yes(1)
   X='​ralph',​ Y='​howard'​   X='​ralph',​ Y='​howard'​
 +</​code>​
 +
 +'''​Input'''​
 +<​code>​
 +Schemes:
 +  Student(name,​ age, class)
 +Facts:
 +  Student('​Sean','​21','​Sophomore'​).
 +  Student('​Arthur','​19','​Freshman'​).
 +  Student('​Sidney','​19','​Sophomore'​).
 +  Student('​Nicole','​23','​Senior'​).
 +Rules:
 +Queries:
 +  Student(A,'​19',​B)?​
 +  Student(M,​M,​M)?​
 +  Student('​Nicole',​howOld,'​Senior'​)?​
 +</​code>​
 +
 +'''​Output'''​
 +<​code>​
 +Student(A,'​19',​B)?​ Yes(2)
 +  A='​Arthur',​ B='​Freshman'​
 +  A='​Sidney',​ B='​Sophomore'​
 +Student(M,​M,​M)?​ No
 +Student('​Nicole',​howOld,'​Senior'​)?​ Yes(1)
 +  howOld='​23'​
 </​code>​ </​code>​
  
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 Here is a simple strategy to consider when deciding how to evaluate queries: Here is a simple strategy to consider when deciding how to evaluate queries:
-# Iterate through every parameter of the query and perform a select for every constant and every variable that has occurred before. +# Iterate through every parameter of the query and perform a select for every constant and every variable that has occurred before. ​It may be the case that no select takes place on a certain variable or any variable in a query, which is fine! 
-# Once all the select operations have been completed, project the relation to only include ​attributes for original variables ​(only the first instance of each variable, leaving out the constants and duplicate instances of variables)+# Once all the select operations have been completed, project the relation to include ​only columns with identifiers in the query (only the first instance of each variable, leaving out the columns that were selected for constants and the columns that were selected as the duplicate instances of variables)
 # After projecting, rename those attributes to their new names as given in the query. # After projecting, rename those attributes to their new names as given in the query.
-The strategy implies that each select knows the list of IDs in the final project ​since it needs to check for duplicates ​to determine when to select on a column rather than a constant. Also in this strategy, it may be the case that no select takes place on an ID parameter (which is just fine).+The functions must be called ​in this order: any selects, followed by a project, followed by a rename. While it is possible in some circumstances ​to do it in a different order, such attempts will often lead to errors, so you need to execute these functions ​in the proper order.
  
 '''​What does the select operation do?'''​ '''​What does the select operation do?'''​
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 # It can find all the tuples that have the same value in two columns (doesn'​t matter what that value is, as long as the two columns both have it). # It can find all the tuples that have the same value in two columns (doesn'​t matter what that value is, as long as the two columns both have it).
 The schema stays the same. The schema stays the same.
 +
 +'''​If the select operation finds when two columns have the same value, should it also find when two columns have different values?'''​
 +
 +No. If a query has two different variables in it, that does not mean the select must find tuples with different values in those columns. Consider the last query of the first example:
 +
 +<​code>​
 +SK(A,B)? Yes(3)
 +  A='​a',​ B='​c'​
 +  A='​b',​ B='​b'​
 +  A='​b',​ B='​c'​
 +</​code>​
 +
 +While A and B are different variables, the query still includes when the values are the same in the tuple (the second result where both A and B equal '​b'​).
  
 '''​What does the project operation do?'''​ '''​What does the project operation do?'''​
  
-The project operation changes the number and order of columns in a relation. The resulting relation will have either the same number or fewer columns. This affects the schema and all of the tuples in that relation.+The project operation changes the number and order of columns in a relation. The resulting relation will have either the same number ​of or fewer columns. This affects the schema and all of the tuples in that relation.
  
 '''​Why can the project operation also re-order the tuple?'''​ '''​Why can the project operation also re-order the tuple?'''​
cs-236/relational-database.1508975558.txt.gz · Last modified: 2017/10/25 23:52 by jrtyler
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