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Material for Database Class.
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Subject Hash Author Date (UTC)
Crystal's final edits. 714e3030423a836c4ba07890f9aa5e45f58ad15a aubert@math.cnrs.fr 2020-05-21 17:43:26
Converted an image into a figure (Movie example). c55e61ed5d11631e908d99b14ef10a0a0247bda0 aubert@math.cnrs.fr 2020-05-20 20:58:41
Re-formatted SQL code. 915442a1ba4d8baa120343f98de5ee39d4ac45f6 aubert@math.cnrs.fr 2020-05-18 15:52:06
Fixed Known_bugs 5900c572928ec3b8c98c82fe4e95ebbe9aeee6c3 aubert@math.cnrs.fr 2020-05-15 18:19:36
Fixed contrib and enriched example. 04864c0ee2d4fa77b4e681ebf8049c4642bf1e67 aubert@math.cnrs.fr 2020-05-15 18:17:22
Fixed formatting mistake. 948a87c75b5d9aa8317feb5a0859d4efc23e95d6 aubert@math.cnrs.fr 2020-05-15 17:58:40
Cleaned SQL code. 4d39ebc5c1a3566ef4d3fa7afc8b2868f827c108 aubert@math.cnrs.fr 2020-05-15 17:41:00
Fixing few mistakes in code. b7eb7a0e476f8e0c3c6d3e651fd80827a03dd127 aubert@math.cnrs.fr 2020-05-15 17:38:32
Fixing few mistakes in code. 2bc77d7ee4e82e6961ce123fb7c3e1c68cba59b5 aubert@math.cnrs.fr 2020-05-15 17:30:02
Testing and indenting SQL code. a2b3bb4e242dd4980b94b25d11d6001459e2f0a0 aubert@math.cnrs.fr 2020-05-15 17:26:27
Clarified an example. e68bac453ab427c132b55249e21a08166b112f31 aubert@math.cnrs.fr 2020-05-15 15:06:54
Edits in style. 47578b081f74e9ec706772fa70a3079957129542 aubert@math.cnrs.fr 2020-05-15 14:38:16
Added activity diagram. 11c9acfa88c398f7463d6e54f45ea48c8793caf1 aubert@math.cnrs.fr 2020-05-15 14:34:31
Added activity diagram. 995cf4f64c43601716f77bb46d1535025ea14d10 aubert@math.cnrs.fr 2020-05-15 14:33:30
Edits in intro, converted an image to a figure for example of class diagram. 1ff4ef2f7f44ece81972a6c77e9f6654c144fcdc aubert@math.cnrs.fr 2020-05-14 22:12:38
Adding example file, to test installation. 5ed35e64a4e4dc60c888358bde54594999aab34d aubert@math.cnrs.fr 2020-05-13 19:03:41
Minor adjustments to the syllabus. dca6f12d9d3d561755991029f2d53bf9823a8cea aubert@math.cnrs.fr 2020-05-13 19:02:41
Worked on reverse-engineering section. 34aeba178fe553c08b4fb3738523be293704e09d aubert@math.cnrs.fr 2020-05-13 18:52:09
Cleaning images. ac02dcf8ffbbbd24139491e5d1e349ace782401e aubert@math.cnrs.fr 2020-05-13 17:40:43
Started to spell-check… 799dc31237aa41176687f37306ca4092a7760f89 aubert@math.cnrs.fr 2020-05-13 17:17:06
Commit 714e3030423a836c4ba07890f9aa5e45f58ad15a - Crystal's final edits.
Author: aubert@math.cnrs.fr
Author date (UTC): 2020-05-21 17:43
Committer name: aubert@math.cnrs.fr
Committer date (UTC): 2020-05-21 17:43
Parent(s): c55e61ed5d11631e908d99b14ef10a0a0247bda0
Signer:
Signing key:
Signing status: N
Tree: 15c8da3a3d87f05b2ede26f108ccc7abc0ea7009
File Lines added Lines deleted
notes/lectures_notes.md 118 81
File notes/lectures_notes.md changed (mode: 100644) (index 068ea8b..59efc24)
... ... Example of Use Case
5910 5910
5911 5911 Exercise +.# Exercise +.#
5912 5912
5913 : Name the three high-level models we will be looking at in this class (expanding the acronyms).
5913 : Name the three high-level models we will be learning about in this class (expand the acronyms).
5914 5914
5915 5915 Exercise +.# Exercise +.#
5916 5916
 
... ... Exercise +.#
5922 5922
5923 5923 Exercise +.# Exercise +.#
5924 5924
5925 : Draw the ER diagram for a "CELLPHONE" entity that has a composite attribute "Plan" (decomposed into "Carrier" and "Price"), a "Mobile\_identification\_number" key attribute, and a multi-valued "App\_Installed" attribute.
5925 : Draw the ER diagram for a "CELLPHONE" entity that has a composite attribute "Plan" (decomposed into "Carrier" and "Price"), an "MIN" (Mobile Identification Number) key attribute, and a multi-valued "App\_Installed" attribute.
5926 5926
5927 5927 Exercise +.# Exercise +.#
5928 5928
5929 : Name one difference between a primary key in the relational model, and a key attribute in the ER model.
5929 : Name one difference between a primary key in the relational model and a key attribute in the ER model.
5930 5930
5931 5931 Exercise +.#derived Exercise +.#derived
5932 5932
 
... ... Exercise +.#derived
5935 5935
5936 5936 Exercise +.# Exercise +.#
5937 5937
5938 : Invent an entity type with at least one composite attribute and one atomic attribute, but no multi-valued attribute, identify a possible key attribute, and draw the entity type you obtained using the conventions we used in class.
5938 : Invent an entity type with at least one composite attribute and one atomic attribute, but no multi-valued attributes. Identify a possible key attribute and draw the entity type you obtained using the conventions we used in class.
5939 5939
5940 5940 Exercise +.# Exercise +.#
5941 5941
 
... ... Exercise +.#recursive
5947 5947
5948 5948 Exercise +.# Exercise +.#
5949 5949
5950 : What does it mean for a binary relationship type "Owner" between entity types "Person" and "Computer" to have a cardinality ration $M:N$?
5950 : What does it mean for a binary relationship type "Owner" between entity types "Person" and "Computer" to have a cardinality ratio of $M:N$?
5951 5951
5952 5952 Exercise +.# Exercise +.#
5953 5953
 
... ... Exercise +.#
5958 5958
5959 5959 Draw a diagram to represent a relationship type $R$ between two entities types $A$ and $B$ such that: Draw a diagram to represent a relationship type $R$ between two entities types $A$ and $B$ such that:
5960 5960
5961 - An entity in $A$ may or may not be in relationship $R$ with an entity in $B$,
5962 - An entity in $B$ must be in relationship $R$ with an entity in $A$,
5963 - An entity in $A$ can be in relationship through $R$ with at most one entity in $B$,
5964 - An entity in $B$ can be in relationship through $R$ with any number of entities in $A$.
5961 - An entity in $A$ may or may not be in relationship $R$ with an entity in $B$.
5962 - An entity in $B$ must be in relationship $R$ with an entity in $A$.
5963 - An entity in $A$ can be in relationship $R$ with at most one entity in $B$.
5964 - An entity in $B$ can be in relationship $R$ with any number of entities in $A$.
5965 5965
5966 5966 Exercise +.# Exercise +.#
5967 5967
 
... ... Exercise +.#
5970 5970
5971 5971 Exercise +.#chair_relationship Exercise +.#chair_relationship
5972 5972
5973 : What does it mean for a binary relationship type "Chair" between entity types "Professor" and "Department" to have a cardinality ratio 1:N?
5974 Would it make sense to be have a total participation constraint on one side, and if yes, on which one?
5973 : What does it mean for a binary relationship type "is the Chair of" between entity types "Professor" and "Department" to have a cardinality ratio of 1:N?
5974 Would it make sense to be have a total participation constraint on one side, and if yes, on which side?
5975 5975
5976 5976 Exercise +.# Exercise +.#
5977 5977
 
... ... Exercise +.#
5996 5996
5997 5997 Exercise +.# Exercise +.#
5998 5998
5999 : Give an example of a binary relationship type of cardinality $N:1$, and draw the corresponding diagram (you do not have to include details on the participating entity types).
5999 : Give an example of a binary relationship type of cardinality $N:1$ and draw the corresponding diagram (you do not have to include details on the participating entity types).
6000 6000
6001 6001 Exercise +.# Exercise +.#
6002 6002
6003 : Draw an ER diagram with a single entity type, with two stored attributes and one derived attribute. In your answer, it should be clear that the value for the derived attribute can always be obtained from the value(s) for the other attribute(s).
6003 : Draw an ER diagram with a single entity type, with two stored attributes, and one derived attribute. In your answer, it should be clear that the value for the derived attribute can always be obtained from the value(s) of the other attribute(s).
6004 6004
6005 6005 Exercise +.# Exercise +.#
6006 6006
6007 : Draw an ER diagram expressing the total participation of an entity type "BURGER" in a binary relation "CONTAINS" between "BURGER" and "INGREDIENT".
6008 What would be the ratio of such a relation?
6007 : Draw an ER diagram expressing the total participation of an entity type "BURGER" in a binary relation "CONTAINS" with an entity type "INGREDIENT".
6008 What would be the cardinality ratio of such a relation?
6009 6009
6010 6010 Exercise +.# Exercise +.#
6011 6011
6012 : Under what condition(s) can an attribute of a binary relationship type be migrated to become an attribute of one of the participating entity type?
6012 : Under what condition(s) can an attribute of a binary relationship type be migrated to become an attribute of one of the participating entity types?
6013 6013
6014 6014 Exercise +.# Exercise +.#
6015 6015
6016 6016 : Suppose a "PRODUCES" relationship with an attribute "Amount" exists between a "PRODUCER" entity type and a "MOVIE" entity type, with ratio $1:M$. : Suppose a "PRODUCES" relationship with an attribute "Amount" exists between a "PRODUCER" entity type and a "MOVIE" entity type, with ratio $1:M$.
6017 Migrate the "Amount" attribute to one of the entity type and draw the resulting diagram.
6017 Migrate the "Amount" attribute to one of the entity types and draw the resulting diagram.
6018 6018
6019 6019 Exercise +.# Exercise +.#
6020 6020
6021 6021 : Suppose a "MEMBERSHIP relationship with an attribute "Level" (e.g., "silver", "platinium", etc.) exists between a "PERSON" entity type and a "CLUB" entity type, with ratio $M:1$. : Suppose a "MEMBERSHIP relationship with an attribute "Level" (e.g., "silver", "platinium", etc.) exists between a "PERSON" entity type and a "CLUB" entity type, with ratio $M:1$.
6022 Migrate the "Level" attribute to one of the entity type and draw the resulting diagram.
6022 Migrate the "Level" attribute to one of the entity types and draw the resulting diagram.
6023 6023
6024 6024 Exercise +.# Exercise +.#
6025 6025 ~ ~
6026 6026
6027 Below, you can specify roles names in your diagrams for added clarity, and remember to list **all** the constraints.
6028 6027 Assume with have three entity types, "Lecture Notes", "Class" and "Professor." Assume with have three entity types, "Lecture Notes", "Class" and "Professor."
6029 Give
6030 6028
6031 #. One example of a ternary relationship between them,
6032 #. Two examples of binary relationships between any two of them,
6033 #. A question that could be answered using one model but not the other (and specify which relationship would be able to answer your question).
6029 #. Draw a diagram of a ternary relationship between the three entities.
6030 #. Draw a diagram that has two binary relationships from one of the three entities to the other two entities.
6031 #. Come up with a question that could be answered using one model but not the other from the previous steps (specify which relationship would be able to answer your question).
6034 6032
6033 You can specify role names in your diagrams for added clarity, and remember to list **all** the constraints.
6034
6035 6035 Exercise +.#ternary Exercise +.#ternary
6036 6036
6037 6037 : Can we always replace a ternary relationship with three binary relationships? Give an example. : Can we always replace a ternary relationship with three binary relationships? Give an example.
 
... ... Exercise +.#
6239 6239
6240 6240 Solution +.# Solution +.#
6241 6241
6242 : **U**nified **M**odeling **L**anguage, **E**ntity **R**elationship and **E**nhanced **E**ntity–**R**elationship models.
6242 : The three high-level models we will be learning about are the **U**nified **M**odeling **L**anguage, **E**ntity **R**elationship, and **E**nhanced **E**ntity–**R**elationship models.
6243 6243
6244 6244 Solution +.# Solution +.#
6245 6245
6246 : Name / extension.
6247 To have statistics about the extensions, to sort the username by length, etc.
6246 : A useful decomposition of an email address attribute could be: the username part before the @ sign, and the domain part afterwards.
6247 It might be useful to have statistics about the domains of the users or to sort the usernames by length, etc.
6248 6248
6249 6249 Solution +.# Solution +.#
6250 6250
 
... ... Solution +.#
6262 6262 Solution +.# Solution +.#
6263 6263
6264 6264 ~ ~
6265 A derived attribute is an attribute whose value can be determined by the value of other attributes. For instance,
6266 - The value of an "Age" attribute could be determined from the value of an "Date of birth" attribute and the current day.
6267 - The value of an "State" attribute can be determined from the value of a "Zip code" attribute.
6268 - The value of a "Body Mass Index" attribute could be calculated from the values of height and weight attributes.
6269 - The value of a "Initials" attribute could be determined using the values of the "First Name", "Middle Name" and "Last Name" attributes.
6265 A derived attribute is an attribute whose value can be determined by the value of other attributes. For instance:
6266 - The value of an "Age" attribute could be determined from the value of an "Date of birth" attribute and the current day.
6267 - The value of a "State" attribute can be determined from the value of a "Zip code" attribute.
6268 - The value of a "Body Mass Index" attribute could be calculated from the values of height and weight attributes.
6269 - The value of an "Initials" attribute could be determined using the values of the "First Name", "Middle Name", and "Last Name" attributes.
6270 6270
6271 6271 Solution +.# Solution +.#
6272 6272
 
... ... Solution +.#
6274 6274
6275 6275 Solution +.# Solution +.#
6276 6276
6277 : The number of participating entity types.
6277 : The degree of a realationship type is the number of its participating entity types.
6278 6278
6279 6279 Solution +.# Solution +.#
6280 6280
6281 : A relationship type where the same entity type participates more than once.
6282 On seats, "is to the left of", on persons, "is married to".
6281 : A self-referencing relationship type is where the same entity type participates more than once.
6282 On a SEATS entity type, it would be an attribute like "is to the left of" or on a PERSONS entity type, it would be and attribute like "is married to".
6283 6283
6284 6284 Solution +.# Solution +.#
6285 6285
6286 : That a person can own multiple computers, and that a computer can have multiple owners.
6286 : The cardinality ratio on the binary relationship type "Owner" between the entity types "Person" and "Computer" means that a person can own multiple computers, and a computer can have multiple owners.
6287 6287
6288 6288 Solution +.# Solution +.#
6289 6289
6290 : Cardinality ration and participation constraints.
6290 : The two possible structural constraints on a relationship type are the cardinality ratio and participation constraints.
6291 6291
6292 6292 Solution +.# Solution +.#
6293 6293 ~ ~
6294 We would obtain the following drawing:
6294 We would obtain the following diagram:
6295 6295
6296 6296 ![](fig/er/abstract) ![](fig/er/abstract)
6297 6297
6298 6298 Solution +.# Solution +.#
6299 6299
6300 6300 : A key opens only one door, and every key must open at least one door. : A key opens only one door, and every key must open at least one door.
6301 A door can be opened by multiple key, and some doors may not be opened by keys (think of doors that cannot be locked).
6301 A door can be opened by multiple keys, and some doors may not be opened by any key (think of doors that do not have a lock).
6302 6302
6303 6303 Solution +.# Solution +.#
6304 6304
6305 : It means that a department can have at most one professor being its chair, but that a professor can be the chair of multiple departments.
6306 It could make sense to require that every department has a chair, hence writing a double line between the Department entity and the Chair relationship, but it would not make sense to have a total participation constraint on the side of the professor (which would mean that every professor _has to_ chair a department).
6305 : The binary relation type "is the Chair of" with a cardinality ratio of 1:N between entity types "Professor" and "Department" means that a department can have at most one professor as its chair, but that a professor can be the chair of multiple departments.
6306 It could make sense to require that every department has a chair, hence writing a double line between the Department entity and the "is the Chair of" relationship, but it would not make sense to have a total participation constraint on the side of the professor (which would mean that every professor _has to_ be the chair of a department).
6307 6307
6308 6308 Solution +.# Solution +.#
6309 6309
6310 6310 : An operating system may be supported by many computers, but it is also possible that no computer supports it (think of an operating system in development, or developed for embeded devices). : An operating system may be supported by many computers, but it is also possible that no computer supports it (think of an operating system in development, or developed for embeded devices).
6311 A computer must support at least one operating system, and can support multiple operating systems.
6311 A computer must support at least one operating system and can support multiple operating systems.
6312 6312
6313 6313 Solution +.# Solution +.#
6314 6314 ~ ~
 
... ... Solution +.#
6319 6319 CAR | $1:1$ | TAG | "A car has exactly one tag, a tag belongs to one particular car." CAR | $1:1$ | TAG | "A car has exactly one tag, a tag belongs to one particular car."
6320 6320 INSTRUCTOR | $1:N$ | LECTURE | "An instructor can teach multiple lecture, but a lecture is taught by only one person." INSTRUCTOR | $1:N$ | LECTURE | "An instructor can teach multiple lecture, but a lecture is taught by only one person."
6321 6321 INSTRUCTOR | $1:N$ | OFFICE | "An instructor can have multiple office, but an office belongs to only one instructor" INSTRUCTOR | $1:N$ | OFFICE | "An instructor can have multiple office, but an office belongs to only one instructor"
6322 COMPUTER | $M:N$ | OS| "A computer can have multiple operating system, the same operating system can be installed on more than one computer."
6322 COMPUTER | $M:N$ | OPERATING_SYSTEM| "A computer can have multiple operating system, the same operating system can be installed on more than one computer."
6323 6323
6324 Some of those choices, of course, are arguable (typically, almost any combination seems reasonnable for the INSTRUCTOR : OFFICE relation).
6324 Some of these choices are debatable (typically, almost any combination seems reasonable for the INSTRUCTOR : OFFICE relation).
6325 6325
6326 6326 Solution +.# Solution +.#
6327 6327
6328 : SUPERVISION, a recursive relationship on EMPLOYEE.
6328 : A binary of relationship of SUPERVISOR as a recursive relationship on EMPLOYEE.
6329 6329
6330 6330 Solution +.# Solution +.#
6331 6331
 
... ... Solution +.#
6341 6341
6342 6342 Solution +.# Solution +.#
6343 6343
6344 : When the cardinality is $1:N$, $1:1$ or $N:1$, the attribute on the relationship can be migrated "to the $N$ side", or to either side, if there is none.
6345 Note that for $n$-ary relationships, at most all but one ratio needs to be $1$ for the attribute to be allowed to migrate (and, again, "to the $N$ side", or to any side, if there is none).
6344 : An attribute of a binary relationship type can be migrated to one of the participating entity types when the cardinality ratio is $1:N$, $1:1$, or $N:1$. It can be migrated "to the $N$ side" or, if there is no $N$ side, to either side.
6345 Note that for $n$-ary relationships, at least one ratio needs to be $1$ for the attribute to be allowed to migrate (and "to the $N$ side", or, if there is no $N$ side, to any side).
6346 6346
6347 6347
6348 6348 Solution +.# Solution +.#
 
... ... Solution +.#
6361 6361
6362 6362 Solution +.# Solution +.#
6363 6363 ~ ~
6364 #. A possible example of ternary relationship is:
6364
6365 #. A possible example of ternary relationship is:
6365 6366
6366 6367 ![](fig/er/ternary_lecture_notes) ![](fig/er/ternary_lecture_notes)
6367 ~
6368 ~
6368 6369
6369 #. Two binary relationships could be:
6370 #. One example of two binary relationships could be:
6370 6371
6371 6372 ![](fig/er/binary_lecture_notes) ![](fig/er/binary_lecture_notes)
6372 6373 ~ ~
 
... ... Solution +.#
6380 6381
6381 6382 > "What are the lecture notes refered to by Prof. X in their class Y?" > "What are the lecture notes refered to by Prof. X in their class Y?"
6382 6383
6383 could not be answered using the binary relationships (since we not know what classes are taught by Prof. X).
6384 could not be answered using the binary relationships (since we do not know what classes are taught by Prof. X).
6384 6385
6385 6386 Solution +.# Solution +.#
6386 6387
 
... ... Solution +.#
6451 6452
6452 6453 Solution +.# Solution +.#
6453 6454
6454 : Just because a coincidence exists (i.e., "in my data set, no android user is color-blind") does not mean that it will always be true (i.e., "no color-blind person will ever use android"). Functional dependencies should come from a principled reasonning about the attributes, and not from the observation of the data.
6455 : Just because a coincidence exists (i.e., "in my data set, no android user is color-blind") does not mean that it will always be true (i.e., "no color-blind person will ever use android"). Functional dependencies should come from a principled reasoning about the attributes, and not from the observation of the data.
6455 6456
6456 6457 Solution +.# Solution +.#
6457 6458 ~ ~
 
... ... You can also have a look at the end of `code/java/AdvancedProg.java`, which crea
8072 8073
8073 8074 Exercise +.# Exercise +.#
8074 8075
8075 : What are the technologies that makes it possible for a Java application to communicate with a DBMS?
8076 : What are the technologies that make it possible for a Java application to communicate with a DBMS?
8076 8077
8077 8078 Exercise +.# Exercise +.#
8078 8079
 
... ... Exercise +.#
8122 8123
8123 8124 Exercise +.# Exercise +.#
8124 8125
8125 : In what class is the `getColumnName` method?
8126 : In what class is the `getColumnName()` method?
8126 8127
8127 8128
8128 8129 Exercise +.# Exercise +.#
8129 8130 ~ ~
8130 8131
8131 Assuming `stmt`{.java} is a `Statement`{.java} object, in the statement
8132 Assuming `stmt`{.java} is a `Statement`{.java} object, in the statement:
8132 8133
8133 8134 ```{.java} ```{.java}
8134 8135 modif = stmt.executeUpdate(strC); modif = stmt.executeUpdate(strC);
8135 8136 ``` ```
8136 what is
8137 What is...
8137 8138
8138 #. the datatype of `modif`{.java}?
8139 #. the datatype of `strC`{.java}?
8140 #. a(n example of a) possible value for `strC`{.java}?
8139 #. ... the datatype of `modif`{.java}?
8140 #. ... the datatype of `strC`{.java}?
8141 #. ... a possible value for `strC`{.java}?
8141 8142
8142 8143
8143 8144 Exercise +.# Exercise +.#
 
... ... Exercise +.#
8147 8148
8148 8149 Exercise +.# Exercise +.#
8149 8150
8150 : Assuming `ps` is the prepared statement `INSERT INTO EXAM VALUES (?, ?)`, write the three statements needed to allocate "Quiz" and "5" to the two slots, and then to execute the prepared statement on the database.
8151 : Assume `ps` is the prepared statement:
8152
8153 ```{.java}
8154 INSERT INTO EXAM VALUES (?, ?);
8155 ```
8156 Write the three statements needed to allocate "Quiz" and "5" to the two slots and to execute the prepared statement in the database.
8151 8157
8152 8158 Exercise +.#ErrorsInCode Exercise +.#ErrorsInCode
8153 8159 ~ ~
8154 8160
8155 8161 In the code below, there are five errors between line 13 and line 32. In the code below, there are five errors between line 13 and line 32.
8156 8162 They are *not* subtle Java errors (like misspelling a key word) and do not come from the DBMS (so you should assume that the password is correct, that the database exists, etc.). They are *not* subtle Java errors (like misspelling a key word) and do not come from the DBMS (so you should assume that the password is correct, that the database exists, etc.).
8157 For each error, highlight it precisely and give a short explanation.
8163 Highlight each error and explain why it is an error.
8158 8164
8159 8165 ```{.java .numberLines include=code/java/ProgWithErrors.java} ```{.java .numberLines include=code/java/ProgWithErrors.java}
8160 8166 ``` ```
8161 8167
8162 8168 Exercise +.# Exercise +.#
8163 8169
8164 : Write a small program that determine whenever the `null` value from Java is equal to the `NULL` value in your DBMS.
8170 : Write a program that determines if the `null` value from Java code is equal to the `NULL` value in the DBMS.
8165 8171
8166 8172 ## Solution to Exercises {-} ## Solution to Exercises {-}
8167 8173
8168 8174 Solution +.# Solution +.#
8169 8175
8170 : API's and driver's to implement them.
8176 : The technologies theat make it possible for a Java application to communicate with w DBMS are API's and the drivers to implement them.
8171 8177
8172 8178 Solution +.# Solution +.#
8173 8179
 
... ... Solution +.#
8175 8181
8176 8182 Solution +.# Solution +.#
8177 8183
8178 : You can find them listed at <https://docs.oracle.com/javase/7/docs/api/java/sql/package-summary.html>. We have used `Connection`, `DatabaseMetaData`, `ResultSetMetaData`, `PreparedStatement`, and `Statement` to name a few.
8184 : There are many classes in the SQL API if Java. There are `Connection`, `DatabaseMetaData`, `ResultSetMetaData`, `PreparedStatement`, and `Statement` to name a few. You can find them listed at <https://docs.oracle.com/javase/7/docs/api/java/sql/package-summary.html>.
8179 8185
8180 8186 Solution +.# Solution +.#
8181 8187
8182 : DriverManager.getConnection()
8188 : The JDBC method that must be called to connect to a database is DriverManager.getConnection()
8183 8189
8184 8190 Solution +.# Solution +.#
8185 8191
8186 : A `Statement` object is used to create a `ResultSet` object, e.g. by calling the `executeQuery` method.
8192 : The class of the object used to create a `ResultSet` object is the `Statement` class. A `Statement` object is used to create a `ResultSet` object, e.g. by calling the `executeQuery` method.
8187 8193
8188 8194 Solution +.# Solution +.#
8189 8195
8190 8196 : The `next()` method checks if there is data to read and, if there is, it moves the cursor to read it. : The `next()` method checks if there is data to read and, if there is, it moves the cursor to read it.
8191 Its return type is a Boolean.
8197 Its return type is Boolean.
8192 8198
8193 8199 Solution +.# Solution +.#
8194 8200
8195 : Using `.executeQuery(strSelect)`{.java}
8201 : You submit a `SELECT`{.java} statement to the DBMS by using `.executeQuery(strSelect)`{.java}.
8196 8202
8197 8203 Solution +.# Solution +.#
8198 8204
8199 : The `executeUpdate` or `execute` methods can be used to perform an `INSERT` command from our program.
8205 : The `executeUpdate()` or `execute()` methods can be used to perform an `INSERT` command from our program.
8200 8206
8201 8207 Solution +.# Solution +.#
8202 8208
8203 : Before the first line. Using the `next` method.
8209 : The `ResultSet` object's cursor is initially pointing at the position before the first line. We move the cursor forward by using the `next()` method.
8204 8210
8205 8211 Solution +.# Solution +.#
8206 8212
8207 : `first`, `last`, `next`, `previous`, `relative`, `absolute` methods.
8213 : There are many navigation methods provided by `ResulSet`. They are the `first()`, `last()`, `next()`, `previous()`, `relative()`, and `absolute()` methods.
8208 8214
8209 8215 Solution +.# Solution +.#
8210 8216
8211 : Connect to `localhost:3306` and create a new database if needed, and use secure connection.
8217 : This JDBC URL format connects to `localhost:3306`, creates a new database if needed, and uses the secure SSL connection.
8212 8218
8213 8219
8214 8220 Solution +.# Solution +.#
8215 8221
8216 : In `modif = stmt.executeUpdate(strC);`{.java}, `modif` is an integer (the number of rows modified by the query), `strC` is a `String` (a `SQL` command), and an example of value is `DELETE FROM BOOKS Where Price > 0.5`.
8222 : The `getColumnName()` method is in the `ResultSetMetaData` class.
8223
8217 8224
8218 8225 Solution +.# Solution +.#
8219 8226
8220 : `ResultSetMetaData`
8227 : In the statement `modif = stmt.executeUpdate(strC);`{.java}...
8228
8229 #. `modif` is an integer (the number of rows modified by the query).
8230 #. `strC` is a `String` (a `SQL` command).
8231 #. A possible value for `strC` is `DELETE FROM BOOKS Where Price > 0.5`.
8221 8232
8222 8233 Solution +.# Solution +.#
8223 8234
8224 : A prepared statement is a feature used to execute the same (or similar) `SQL` statements repeatedly with high efficiency.
8235 : A prepared statement is a feature used to execute `SQL` statements repeatedly with high efficiency that protects against `SQL` injections.
8225 8236
8226 8237 Solution +.# Solution +.#
8227 8238 ~ ~
 
... ... Solution +.#
8237 8248
8238 8249 The errors are: The errors are:
8239 8250
8240 - line 16, `stmt.executeUpdate(strSelect)`{.java}: `executeUpdate`{.java} cannot be used to perform `SELECT` statements.
8241 - line 21, this error is subtle: we need to display the last record before using `previous()`{.java}, otherwise it would be just skipped. We can fix this using a `do`…`while` loop.
8242 - line 22, `String title = rset.getDouble("title");`{.java}: `getDouble`{.java} returns a `double`{.java}, and hence cannot be stored as a `String`{.java}.
8243 - line 28, `ps.executeQuery()`{.java}: the prepared statement did not received a value for the `?` argument.
8251 - The first highlighted portion is found in the `ResultSet` object creation line and should only be this part:
8252
8253 ```{.java}
8254 stmt.executeUpdate(strSelect);
8255 ```
8256 The error is that the `executeUpdate()` method cannot be used to perform `SELECT` statements.
8257
8258 - The second highlighted portion is found in the while loop condition statement:
8259
8260 ```{.java}
8261 rset.previous()
8262 ```
8263
8264 This error *is* subtle: we need to display the last record before using the `previous()`{.java} method, otherwise it would be skipped. We can fix this using a `do`…`while` loop.
8265
8266 - The third highlighted portion is found in the creation statement for the `String` object named `title`:
8267
8268 ```{.java}
8269 String title = rset.getDouble("title");
8270 ```
8271
8272 The error is that the `getDouble()`{.java} method returns a `double`{.java}, which cannot be stored as a `String`{.java}.
8273
8274 - The fourth highlighted portion is found in the creation statement for the `ResulSet` object named `result`:
8275
8276 ```{.java}
8277 ps.executeQuery();
8278 ```
8279
8280 The error here comes from the previous prepared statement that did not receive a value for the `?`.
8244 8281
8245 You can find the program patched in `code/java/ProgWithErrorsPatched.java`, the (relevant) diff. is:
8282 You can find the corrected program in `code/java/ProgWithErrorsPatched.java`, which looks like:
8246 8283
8247 8284 ```{.bash} ```{.bash}
8248 8285 16c16 16c16
 
... ... Solution +.#
8281 8318 Solution +.# Solution +.#
8282 8319 ~ ~
8283 8320
8284 Here it is:
8321 Here is what the program should look like:
8285 8322
8286 8323
8287 8324 ```{.java .numberLines include=code/java/TestForNull.java} ```{.java .numberLines include=code/java/TestForNull.java}
 
... ... Solution to [%D %n (%T)](#problem:xmltoeraward)
9287 9324 The next difficulty is the status of the award itself: should it be a relationship with many attributes, between the RESEARCHER and INSTITUTION entities? The next difficulty is the status of the award itself: should it be a relationship with many attributes, between the RESEARCHER and INSTITUTION entities?
9288 9325 The issue with this approach is that an award can have multiple investigators, as shown in the example, and that this number can vary. Hence, fixing the arity and constraints on this relationship will be difficult. The issue with this approach is that an award can have multiple investigators, as shown in the example, and that this number can vary. Hence, fixing the arity and constraints on this relationship will be difficult.
9289 9326 We could have a relation of arity `2`, and "duplicate it" if multiple researchers are involved in the same grant, but that seems like a poor choice (since all the information about the grant will need to be duplicated). We could have a relation of arity `2`, and "duplicate it" if multiple researchers are involved in the same grant, but that seems like a poor choice (since all the information about the grant will need to be duplicated).
9290 Therefore, it seems more reasonnable to make the award an entity.
9327 Therefore, it seems more reasonable to make the award an entity.
9291 9328
9292 9329 How should we connect the AWARD entity with the RESEARCHER and INSTITUTION entities? How should we connect the AWARD entity with the RESEARCHER and INSTITUTION entities?
9293 9330 A ternary relation has some drawbacks, since it would require some duplication when multiple investigators are working on the same award. A ternary relation has some drawbacks, since it would require some duplication when multiple investigators are working on the same award.
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