CS A1150 Databases, 2017 Exercise Round 6 (( ), Solutions

Transcription

1 CS A1150 Databases, 2017 Exercise Round 6 (( ), Solutions 1. (6 p.) Consider a database schema which consists of three relations, whose schemas are: Students(ID, name, program, year) Courses(code, name, credits) Grades(studentID, coursecode, date, grade) See Exercise 1 for detailed description of the relations and their attributes. Write the triggers described in parts (a), (b), and (c). After that, test the triggers in part (d). Use SQLite syntax, not SQL standard syntax such that you can test the triggers using SQLiteStudio. (Hint: Instead of writing AFTER UPDATE, it is also possible to write AFTER INSERT or AFTER DELETE when defining triggers.) a) When inserting a row into table Courses, check that the number of credits is not greater than If it is, set the number of the credits of the inserted row to be CREATE TRIGGER CreditsTrigger AFTER INSERT ON Courses WHEN NEW.credits > 10.0 BEGIN UPDATE Courses SET credits = 10.0 WHERE code = NEW.code; END; b) When updating the value of attribute grade of the row in table Grades, check that the new grade is greater than or equal to the old grade. If it is not, restore the grade to what it was before the update. CREATE TRIGGER GradeTrigger AFTER UPDATE OF grade ON Grades WHEN NEW.grade < OLD.grade BEGIN UPDATE Grades SET grade = OLD.grade WHERE studentid = OLD.studentID AND coursecode = OLD.courseCode; END; c) When inserting a row into table Grades, check that the student ID exists in table Students. If it does not, insert in Students a new row with this student ID and NULL as the value of the other attributes. CREATE TRIGGER StudentTrigger AFTER INSERT ON Grades WHEN NEW.studentID NOT IN (SELECT ID FROM Students) BEGIN INSERT INTO Students VALUES(NEW.StudentID, NULL, NULL, NULL); END;

2 d) Use SQLiteStudio and create a new database with the help of the file exampledatabase6.sql given in MyCourses (this database is much simpler than the example database in Exercise Round 2). Write the definitions of the triggers from parts (a), (b) and (c). Write two INSERT statements and one UPDATE statement to test your triggers. List the contens of the tables Students, Grades and Courses both before and after those INSERT / UPDATE statements. An example of the SQL statements that can be used to test the triggers created above: 2. (3 p.) INSERT INTO Courses VALUES( M Z1111, Math for dummies, 12.0); UPDATE Grades SET grade = 2 WHERE studentid = AND coursecode = CS A1111 ; INSERT INTO Grades VALUES( , M Z1111, , 3); a) Give an XML-document (without using attributes), which inludes the following information about a certain professor: her name which is composed of the first name (Maija) and the last name (Lahtinen), the department (Computer Science), the office which is composed of the building (CS) and the room (A166), and the telephone numbers ( and ). <?xml version = "1.0" encoding = "utf-8" standalone = "yes"?> <Professor> <Name> <First_name>Maija</First_name> <Last_name>Lahtinen</Last_name> </Name> <Department>Computer Science</Department> <Office> <Building>CS</Building> <Room>A166</Room> </Office> <Telephone_number> </Telephone_number> <Telephone_number> </Telephone_number> </Professor> b) Give the tree diagram of the document given in part (a). Professor Name Department Name Telephone_ number Telephone_ number First_name Last_name Computer Science First_name Last_name Tero Teekkari Maija Lahtinen 3. (3 p.) Show that any relation R(A 1, A 2,..., A n ) and its instance (the tuples in the relation) can be represented by an XML document. We show it by constructing an XML-document which repsesents an arbitrary instance of a relation R(A 1, A 2,..., A n ). The structure of the document is as follows:

3 We construct a root element Root Inside the root element, we add an R element for each tuple in the instance of R. Inside each R element, we add an element Ai for each attribute A i of R. The text inside this element is the value of the attribute A i in the corresponding tuple. An example: Suppose that the instance of R contains 3 tuples (value11, value12,..., value1n) (value21, value22,..., value2n) (value31, value32,..., value3n) The corresponding XML-document is <?xml version = "1.0" standalone = "yes"?> <Root> <R> <A1>value11</A1> <A2>value12</A2>... <An>value1n</An> </R> <R> <A1>value21</A1> <A2>value22</A2>... <An>value2n</An> </R> <R> <A1>value31</A1> <A2>value32</A2>... <An>value3n</An> </R> </Root> 4. (4 p.) Plan the structure of an XML document containing typical data about courses and their teachers (including the basic information about courses, teachers and who teaches which course in which semester). Give an example XML document. The example document must include at least three courses and two teachers. There are several possibilities. In the following, we have the root element University which has sublements Courses and Teachers. The element Courses has a subelement Course for each course and the element Teachers has a subelement Teacher for each teacher. Information about who teaches which course is stored as subelements of each course. An example XML document: <?xml version = "1.0" encoding = "utf-8" standalone = "yes"?> <University> <Courses> <Course level = "Barchelors"> <Code>CS-A1111</Code> <Name>Basic Course in Programming Y1</Name> <Credits>5.0</Credits> <Teacherinfo> <Taught_by term = "Fall 2015">T222</Taught_by> <Taught_by term = "Fall 2016">T353</Taught_by> </Teacherinfo> <Period>I - II</Period> </Course> <Course level = "Bacherlors"> <Code>CS-A1121</Code> <Name>Basic Course in Programming Y2</Name> <Credits>5.0</Credits> <Teacherinfo> <Taught_by term = "Spring 2016">T353</Taught_by> <Taught_by term = "Spring 2017">T222</Taught_by> </Teacherinfo>

4 <Period>III - V</Period> <Prerequisites>CSE-A1111</Prerequisites> </Course> <Course level = "Masters"> <Code>CS-E5430</Code> <Name>Scalable Cloud Computing</Name> <Credits>5.0</Credits> <Teacherinfo> <Taught_by term = "Fall 2016">T222</Taught_by> </Teacherinfo> <Period>I - II</Period> <Prerequisites>CSE-A1110</Prerequisites> <Prerequisites>CSE-A1140</Prerequisites> </Course> </Courses> <Teachers> <Teacher> <TName>Matti Virtanen</TName> <EID>T222</EID> <Title>Professor</Title> <School>SCI</School> <Department>CS</Department> <Office>B213</Office> <Started> </Started> <Address> <Street>Otakuja 3 C 40</Street> <City>02150 Espoo</City> </Address> <Mail>matti.virtanen@aalto.fi</Mail> </Teacher> <Teacher> <TName>Anna Korhonen</TName> <EID>T353</EID> <Title>University Lecturer</Title> <School>SCI</School> <Department>Phys</Department> <Office>A333</Office> <Started> </Started> <Address> <Street>Servinkuja 2 A 3</Street> <City>02150 Espoo</City> </Address> <Mail>anna.t.korhonen@aalto.fi</Mail> </Teacher> </Teachers> </University> 5. (4 p.) Consider the following DTD. <!DOCTYPE A [ <!ELEMENT A (B*)> <!ELEMENT B (C, D*, E?)> <!ELEMENT C (#PCDATA)> <!ELEMENT D EMPTY> <!ELEMENT E (#PCDATA)> <!ATTLIST A att1 CDATA #IMPLIED att2 CDATA #REQUIRED > <!ATTLIST D att3 CDATA #REQUIRED > ]> Do the XML documents given below follow the DTD above? If they do not, what are the violations (list them all)? a) <?xml version = "1.0" encoding = "utf-8" standalone = "no"?> <!DOCTYPE A SYSTEM "A.dtd"> <A att2 = "value1">

5 <D att3 = "value2"/> <E>some text 2</E> <E>some text 3</E> <D att3 = "value3">some text 4</D> <E>some text 5</E> This document is not valid, because of the following violations: The first B element contains two E elements, although it should contain at most one. The second B element does not contain a C element, although it should contain exactly one. The second D element contains text, although it should be empty. b) <?xml version = "1.0" encoding = "utf-8" standalone = "no"?> <!DOCTYPE A SYSTEM "A.dtd"> <A att1 = "value1"> <D att3 = "value2"/> <D att3 = "value3"/> <C>some text 2</C> <E>some text 3</E> <C>some text 4</C> This document is not valid, because of the following violation: The first A element does not value for attribute att2, although it is required. There are no other violations. 6. (4 p.) Consider the following XML Schema. <?xml version = "1.0" encoding = "utf-8"?> <xs:schema xmlns:xs=" <xs:complextype name = "BType"> <xs:sequence> <xs:element name = "C" type = "xs:string" /> <xs:element name = "D" type = "xs:string" /> </xs:sequence> <xs:attribute name = "att1" type = "xs:integer" use = "required" /> </xs:complextype> <xs:element name = "A"> <xs:complextype> <xs:sequence> <xs:element name = "B" type = "BType" minoccurs = "0" maxoccurs = "unbounded" /> <xs:element name = "E" type = "xs:integer" minoccurs = "1" maxoccurs = "2" /> </xs:sequence> </xs:complextype> </xs:element> </xs:schema>

6 Do the XML documents given below follow the XML Schema above? If they do not, what are the violations? a) <?xml version = "1.0"?> <A> <B att1 = "74"> <C>some text 2</C> <D>some text 3</D> <E>222</E> <E>91</E> <B att1 = "79"> <C>some text 4</C> <E>57</E> <B att1 = "81"> <C>some text 5/C> <D>some text 6</D> This document is not valid because of the following violations: All E elements are subelements of B elements, although they should be subelements of A. The first B element contains two C elements, although it should contain excatly one. The second B element does not contains a D elements, although it should contain excatly one. b) <?xml version = "1.0"?> <A> <D att1 = "77">some text 2</D> <E>12</E> <C>some text 3</C> <D att1 = "36">some text 4</D> <E>44</E> This document is not valid because of the following violations: The first E element should be after all B elements, not between them. B elements do not have values for attribute att1, although they should have. Instead, D elements have value for attribute att1, although they should not. 7. (4 p.) Consider the following XML-document <?xml version = "1.0" encoding = "utf-8" standalone = "yes"?> <Webstore> <Order status = "in post"> <Customernro>556689</Customernro> <Product group = "photography"> <Productnro>T </Productnro> <Name>Canon Ixus 145 </Name> <Price>75.00</Price> <Payment>Invoice</Payment> <Delivery>Post</Delivery> </Order>

7 <Order status = "delivered"> <Customernro>599689</Customernro> <Products> <Product group = "tableware"> <Productnro>T </Productnro> <Name>Arabia Teema plate 15</Name> <Price>12.95</Price> <Amount>6</Amount> <Product group = "photography"> <Productnro>T </Productnro> <Name>Nikon D3200</Name> <Price>359.00</Price> </Products> <Payment>Credit card</payment> <Delivery>Matkahuolto</Delivery> </Order> <Campaign> <Campaignname>Winterbang</Campaignname> <Product group = "photography"> <Productnro>T </Productnro> <Name>Sony Alpha 5000</Name> <Price>390.00</Price> <Leaflets>30000</Leaflets> </Campaign> </Webstore> What are the results of the following XPath queries? Give the complete results. If the result is empty, tell it clearly. a) /Webstore/Order/Product/Price (It is important to include the tags in the result.) <Price>75.00</Price> b) /Webstore/Order//Product/Price (It is important to include the tags in the result.) <Price>75.00</Price> <Price>12.95</Price> <Price>359.00</Price> c) /Webstore/Order/Info (It is important to include the tags in the result.) <Payment>Invoice</Payment> <Delivery>Post</Delivery> <Payment>Credit card</payment> <Delivery>Matkahuolto</Delivery> d) /Webstore//Product[@group = "photography"]/name (It is important to include the tags in the result.) <Name>Canon Ixus 145 </Name> <Name>Nikon D3200</Name> <Name>Sony Alpha 5000</Name>