Support of Relational Algebra Knowledge ... - Hornad - TUKE

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Lex[[MAX]] Lex[[MIN]] Lex[[COUNT]] Lex[[ V ]] Lex[[ . ]] Lex[[ , ]] Lex[[ ( ]] Lex[[ ) ]] Lex[[ + ]] Lex[[ - ]] Lex[[ * ]] Lex[[ / ]] Lex[[ < ]] Lex[[ < ]] Lex[[ > ]] Lex[[ > ]] Lex[[ = ]] Lex[[ != ]] Lexical Unit MAX MIN COUNT RESULT DOT POINT LOZAT POZAT PLUS MINUS MULL DIV LT LE GT GE EQ NE Lex[[ MVi ]] i → ( '0' | .. | '9' ) Lex[[ j 1 … j n ]] j k → ( 'a' | .. | 'z' ) { ( 'a' | .. | 'z' ) } Lex[[ c 1 … c n ]] c k → ( '0' | .. | '9' ) { ( '0' | .. | '9' ) } [( '.' | ',' ) ( '0' | .. | '9' ) {( '0' | .. | '9' )}] Lex[[ ai 1 … i n a ]] i k → znak , a → ” ' “ A set of rules: Terminal Symbol PART ID NM KONST Relation → LOZAT ( ID | PART ) POZAT Function → SUM | AVER | MAX | MIN | COUNT Conditions → Condition {(AND | OR) Condition} Condition → [NOT] (ID (EQ|NE|GT|GE|LT|LE) Query | LOZAT Conditions POZAT) Query → ID | NM | ST | LOZAT Query POZAT | Query Operaction Query Operation → PLUS | MINUS | MUL | DIV It is a context-free grammar. The form of each grammar rule is A → α , where A ∈ Ν a α ∈ ( N U T). On the left side of any rule it is no terminal symbol The grammar is LL(1) grammar, because it satisfies FIRST-FIRST a FIRST-FOLLOW conditions, i.e. for A type rules are defined: A → α1|α2 | ... | αn FIRST-FIRST If α i ⇒ * w, w ∈ T + , α j ⇒ * u, u ∈ T + , then FIRST 1 (α i ) ∩ FIRST 1 (α j ) = ∅ pre 1 ≤ i, j ≤ n, i ≠ j. FIRST-FOLOW If α i ⇒ * e ,t.j. e∈FIRST 1 (α i ) for i, then FIRST 1 (α j )∩FOLLOW 1 (A )=∅ pre 1 ≤ j ≤ n, i ≠ j Program → { PART Command } RESULT Command Command → EQ (Select | Project | JoinAF | Agreg) Select → SEL Conditions Relation Project → PROJ ID { POINT ID } Relation JoinAF → ID ( Join | AF ) Join → JOIN Condition { AND Condition } ( ID | PART ) Agreg → {POINT ID} FUN Function (ID|MUL) {POINT Function (ID|MUL)} Relation IV. IMPLEMENTATION On Figure 1 the scenario of the relational algebra performance is displayed. SQL_RA_Module controls the whole process of RA_queries and select statements treating. Compiler checks RA_query syntax and if any errors occur in parsing SQL_RA_module finishes its evaluation. RA_query is classified as incorrect. Otherwise, a module returns select1_statement which corresponds with student relational algebra query ([5]). The select1_statement is executed on database server ([6][10]). The result relations of select1 and select2 statements are compared. If they are equal a student RA_query is correct else it is incorrect. The module displayed error message if an error occurs in any step of performance.
SequenceDiagram_1 SQL_RA_Module Compiler Database Student RA_query compile select1_statement errors? errors [errors = false]: execute select1 statement result of select1 execute select2 statement result of select2 result of comparison select1 with select2 [errors = true]: compiling error Figure 1 The relational algebra performance scenario V. CONCLUSION Described solution enables to achieve accurate results. It does not compare specified relation query as text but it compares two relations. On the present the basic operations of relational algebra (selection, projection, join, and aggregate function) are implemented. The next operations are developed. The dynamic evaluation of select statement and relational algebra query is the first step of understanding and correct writing of select statement in SQL. ACKNOWLEDGEMENT This work is the result of the project implementation: Knowledge-Based Software Life Cycle and Architectures (Project VEGA No. 1/0350/08) REFERENCES [1] Elmasri,R., Navathe, S.B.: Fundamentals of Database Systems, The Benjamin/Cummings Publishing Company, Inc., 1., 2. editions [2] Codd, E.F.: A Relational Model of Data for Large Shared Data Banks, Communications of the ACM, 1970, p. 377–387 [3] Codd, E.F.: The Relational Model for Database Management (Version 2 ed.). Addison Wesley Publishing Company, 1990 [4] Matiaško, K.: Databázové systémy, EDIS – vydavateľstvo Žilinskej univerzity, 2002, ISBN 80- 7100-968-7 [5] Tóth, M.: Spracovanie relačnej algebry v systéme Moodle, Diploma thesis, Technical University, Košice, 2009 [6] Tóth, M. (2007). SELECT Statement Processing in LMS Moodle, semestral project, Technical University, Košice. [7] Genči, J.: Some consideration about knowledge assessment, 8th Intenational Conference Virtual University VU'07, Bratislava, 13.-14. 12.2007, Bratislava, E-ACADEMIA SLOVACA, 2007, pp. 237-240, ISBN 978-80-89316-09-0 [8] Havlice, Z. (2002). Generovanie jazykových procesorov, Elfa, Kosice 2002, ISBN 80-89066-47- X. [9] Kollár, J., Havlice, Z. (2001). Technológia jazykových systémov, Elfa, Košice 2001, ISBN 80- 89066-12-7. [10] Telepovská Henrieta: SQL STATEMENT KNOWLEDGE ASSESMENT, 6th International Conference on Emerging e-Learning Technologies and Applications, Conference Proceedings, (ICET 2008) Stara Lesna, September 11 – 13, 2008, Kosice, elfa, s.r.o, 2008, str. 181-184, ISBN 978- 80-8086-089-9 [11] Moodle Documentation (2010). http://docs.moodle.org [12] Raadt, M., Dekeyeser, S., Lee, T.Y.: A System Employing Peer Review and Enhanced Computer Assisted Assessment of Querying Skills,
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