AMOS II Tutorial
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1. b AMOS 69 gt select year t from Tournament t where year t gt 1945 The comparison functions lt gt gt and lt are written in infix notation The comparison functions can be applied on numbers strings and any kind of objects The result of comparing two arbitrary OIDs is however undefined actually the internal OID numbers are then compared AMOS 70 gt typenamed Player returns the type having the name Player AMOS 71 gt cardinality typenamed Player returns the number of objects of the type named Player AMOS 72 gt allfunctions typenamed Player returns all currently defined functions where some argument or result is of type Player 9 More about the query language 9 1 Environment variables It is possible to assign the value of a query to an environment variable AMOS 73 gt select c into c from Country c Tournament t where c host t and year t 1982 AMOS 74 gt name c One of the tuples retrieved that fulfill the selection criteria will be assigned If the select statemnt returns many tuples it is undefined which one is assigned 9 2 Examples of queries In the file wcdata amosql there are AMOSQL commands that populate the database Read and exe cute these commands with these commands AMOS 75 gt lt demo wcdata amosq Next follows some examples of somewhat more complicated queries 1 In what tournaments did Sweden participa2. a tour nament while a certain result cannot be returned for more than one value of the input parameter a team can only participate in one tournament Therefore the Bag of declaration is not fully correct The recommended way to represent such a one many relationship is to instead define the inverse func tion to represent the relationship In our case we can define a function tournament instead of 1 A bag is a set where duplicates are allowed Queries in AmosQL and SQL return bags rather than sets participating_teams AMOS 39 gt create function tournament Team gt Tournament as stored The function participating_teams can then be defined as the inverse of tournament AMOS 40 gt create function participating _teams Tournament t gt Team tm as select tm where tournament tm t Cardinality constraints can also constrain the uniqueness of the result of a function The keyword key indicates that a parameter of a stored function is unique thus defining a one one relationship For example the functions year Tournament gt Integer and name Country gt Charstring defined with the commands 3 and 4 have the constraint that the result must be unique This uniqueness can be specified by adding the keyword key after the result parameter To include these cardinality con straints one one relationships the functions should actually have been defined as create function year Tournament gt Integer key as stored cre
3. year Integer host Country 4 3 Objects We are now ready to start populating the database by creating our first objects The following com mand creates three countries i e three instances of the type country AMOS 6 gt create Country instances ita bra esp cita bra and esp are environment variables that are bound to the objects created It is possible to refer to the objects through these variables only during the current transaction They are not stored in the database In the examples below environment variables are used to identify cross referenced objects in the example database For the type Country there is a function name defined The following commands assign names to the three countries i e defines the results of applying the function name on the three just created instances of type country AMOS 7 gt set name ita Italy AMOS 8 gt set name bra Brazil AMOS 9 gt set name esp Spain In the same way we create three instances of type Tournament and define what values the functions year and host return when applied on the objects of type Tournament AMOS 10 gt create Tournament instances t2 t12 t14 AMOS 11 gt set year t2 1934 AMOS 12 gt set host t2 ita AMOS 13 gt set year t12 1982 AMOS 14 gt set host t12 esp AMOS 15 gt set year t14 1990 AMOS 16 gt set host t14 ita The results of the functions can also be defined directly when the objects are created The c
4. AMOS II Tutorial Gustav Fahl and Tore Risch Uppsala Database Laboratory Department of Information Technology Uppsala University Sweden Tore Risch it uu se August 20 2008 revised 2011 02 30 This is an introduction and tutorial to the AMOS II object relational database system AMOS II is a descendant of AMOS which has its roots in a main memory version of Hewlett Packard s DBMS IRIS 1 The entire database is stored in main memory and is saved on disk only through explicit commands AMOS II can be used a single user database a multi user server or as a collection of interacting AMOS II multi database peers In this tutorial only the single user version is described AMOS II is an example of an object relational peer DBMS having a declarative query language AMOSQL For a complete description of AMOS II s functionality see 3 2 1 Introduction To be able to run the examples in the tutorial you need download Amos II zip file to a directory called the Amos directory The unzip will create a subfolders bin demo doc etc The file bin amos2 exe is the executable program and bin amos2 dmp is a database that contains only the data needed by the AMOS II system itself All the commands that are used in the tutorial are in the file demo tutorial amosql In order to try out the queries at the end of the tutorial you also need to load the file demo wcdata amosql AMOS II is started from the OS command window by making the Amos bin dire
5. QL query above is three objects bound to the environame vari ables p1 p2 and p3 Compare this with the query How many teams participated in tournament t 2 AMOS 64 gt count participating_teams t12 In this case the function count is applied once on the entire bag of objects from participating_teams not once per result from participating_teams The reason is that count is defined to take a bag of objects as argument create function count Bag of Object x gt Integer r as Nested queries can be used as arguments to aggregate functions The following command answers the query How many own goals have been made AMOS 65 gt sum select own_goals p m from Player p Match m 8 Miscellaneous 8 1 System functions Several useful functions are predefined in AMOS II See 3 for a complete list of these Here we only give some examples of how they can be used AMOS 66 gt plus 7 4 AMOS 67 gt 7 4 Most arithmetic functions can be written either in prefix or infix notation Other examples of arith metic functions are minus times div and mod AMOS 68 gt max 7 4 max and min returns the largest and the smallest of two objects respectively This is different from maxagg and minagg that return the largest and smallest object from a bag of objects Notice that com parison is defined not only for numbers but actually for any kind of object For example max a b 13 returns the string
6. and Match and participating_teams between Team and Match Let s start with the first relationship Players are participants in games and makes a number goals and a number of own goals in them The most interesting functions are What players participate in a certain match How many goals did a certain player make in a certain match and How many own goals did a certain player make in a certain match create function participating _players Match m gt Player p as create function goals Player p Match m gt Integer g as create function own_goals Player p Match m gt Integer og as It is not recommended to define these functions as stored ones as it would create redundant data We rather store the information about the participation of players in games in a function player_participation and define the three functions above as derived AMOS 50 gt create function player_participations Match gt Bag of Player Integer goals Integer own_goals as stored AMOS 51 gt create function participating_players Match m gt Player p as 1 For example the fact that a player participated in a certain match would have been stored in three dif ferent places 2 No variable names need to be specified after the types in the definitions of stored functions However for clarity we still specify the variable names goals and own_goals 11 select p from Integer g Integer og where player_participations m
7. ate function name Country gt Charstring key as stored This makes it impossible to have two tournaments the same year or to have two countries with the same name The system will raise an error when the constraint is violated For bag valued functions the command add is used for adding values to the results of function The syntax is the same as for the set command AMOS 41 gt create Team represents instances ita82 ita bra82 bra AMOS 42 gt add participating teams t12 1ta82 AMOS 43 gt add participating_teams t12 bra82 AMOS 44 gt name represents participating _teams t12 Notice that a function such as participating_teams which is the inverse of a stored function tourna ment is updatable Normally derived function are not updatable An equivalent way to create the two above teams using the inverse function tournament instead would be create Team represents tournament instances ita82 cita t12 bra82 bra t12 In Amos II when a function returns a bag of values as the inner call to participating_teams in com mand 44 the applied function represents is applied on each element of the result from the set valued function participating_teams This is called Daplex semantics because it was first invented in the functional query language Daplex an ancestor of AmosQL To model the relationship players between Team and Player see Figure 1 we define a function with that name from Team to Player The rela
8. ctory the current directory and then issuing the OS command amos2 You will then enter the AMOS II top loop where you have the prompt Amos 1 gt The number 1 in the prompt the generation number is used for the rollback command explained later In the AMOS II top loop you can issue any AmosQL command to be described below To exit the system issue the command quit Amos 2 gt quit You are assumed to have general knowledge about databases and Entity Relationship modeling 1 1 Styles used in the examples This tutorial uses the following style for the AMOSQL commands you should enter to the AMOS II top loop during the tutorial Amos 4 gt create function name Country gt Charstring as stored AMOSQL commands that are not to be entered but only to serve as examples look like this create type Tournament properties year Integer host Country Thus the AMOSQL commands that are supposed to be executed during the tutorial have the AMOS II prompt with generation number first 2 An example As a running example throughout the overview we use a database to manage information about World Cup tournaments in soccer We start with an extended Entity Relationship schema EER schema that describes the information to be represented in the database The steps how to implement the database in AMOS II are then gradually introduced as the database is built The ER schema is shown in Figure 1 In Section 2 1 the corresponding
9. database description is made in natural language The building blocks of the EER schema are represented by the following corresponding building blocks in the Amos II data model 1 Entity types are represented as types in Amos II 2 Relationships are represented as functions The arrows in the EER diagram indicate the logical direction of the Amos II functions representing the relationships from argument to result 3 Attributes are represented as functions too Cardinality constraints are specified on functions by a special syntactic construct Bag of key 2 1 Database description World Cup tournaments in soccer are arranged every fourth year Each tournament is arranged by some country In each tournament a number of teams participate and they represent various countries Each tournament contains a number of games matches each played between two teams The team that made most goals wins Each game is refereed by a referee and a certain number of spectators come to look at it Each team contains a set of players For each game played by a team of players a subset of these players are chosen to play in this particular match A player can make a number of goals and a number of own goals in a certain game Person Referee Player N represents 1 participating teams Country 1 i N oD Tournament lt host gt Entity type in Amos I
10. e of a certain country here the country object ita one makes the query name ita Sometimes one might also be interested in the inverse function i e a function from names to countries create function country_named Charstring cn gt Country c as select c from Country c where name c cn Alternatively since the variable c is declared also in the function result the function country_named can be formulated without from as create function country_named Charstring cn gt Country c as select c where name c cn The database can then alternatively be populated by these commands set country_named Italy ita set country_named Brazil bra set country_named Spain esp One may get the name of the country object ita by the query select cn from Charstring cn where country_named cn ita In general if one thinks that several functions are useful there is always the possibility to define one of them as a stored base function and then define the others as derived from the base function as in our example 7 3 More function definitions We define some more functions from Figure 1 AMOS 35 gt create function represents Team gt Country as stored AMOS 36 gt create function refereed_by Match gt Referee as stored AMOS 37 gt create function played_in Match gt Tournament as stored AMOS 38 gt create function spectators Match gt Integer as stored 7 4 Bag valued functions and cardinality cons
11. l y Direction of function Se Attribute function in Amos Il yi Inheritance Figure 1 Extended ER schema describing the information in the World Cup database 3 Practical advises 3 1 Rollback The database can be restored to an earlier state by the command rollback generation number For example after the following command all changes from command 4 and forward are undone rollback 4 3 2 Reading commands from a file AMOSQL commands can be read from a file and executed by the AmosQL command lt file name For example the AMOSQL commands for creating the tutorial database are stored in the file tutorial amosql To read an execute all commands in the file demo tutorial amosq when the current folder is the AmosII bin directory execute the command Amos 1 gt lt demo tutorial amosq Notice that in order to learn AMOSQL you are recommended not load the entire script but to copy one command at the time from the file demo tutorial amosql Use cut and paste for this 3 3 Saving a database A database can be saved in the file named file name by the command save file name To create the tutorial database and save it in the file wc dmp do the following amos2 Amos 1 gt lt demo tutorial amosql Amos 2 gt save wc dmp Amos 1 gt quit To start AMOS II with the saved database give the following command to the Windows command window amos2 file name For example amo
12. lowing command answers the query What years did Italy arrange the World Cup AMOS 20 gt select year t from Tournament t where name host t Italy As the final query example the following command answers the query What years were the World Cup arranged and who were its hosts AMOS 21 gt select year t name host t from Tournament t 6 More about types 6 1 Type Hierarchy The types in AMOS II are arranged in a type hierarchy If a type A is defined as a subtype of a type B then the type A inherits all the functions defined on type B In our example the entity types Referee and Player are subtypes of the entity type Person that has an attribute name AMOS 22 gt create type Person AMOS 23 gt create type Referee under Person AMOS 24 gt create type Player under Person The attribute name is represented as a function name from persons to strings AMOS 25 gt create function name Person gt Charstring as stored The function name is now defined on the types Person Referee and Player since Referee and Player are subtypes of Person If a type A is defined as a subtype of a type B it means that all instances of type A automatically become instances type B as well To illustrate this create the following instances of type Person Ref eree and Player AMOS 26 gt create Person name instances Pavel Smerdjakov AMOS 27 gt create Referee name instances r1 Abraham Klein AMOS 28 gt create Pla
13. ommands 6 16 are equivalent with create Country name instances ita Italy bra Brazil spa Spain create Tournament year host instances t2 1934 ita t12 1982 esp t14 1990 ita 5 Query Language Similarly to SQL AMOSQL is a combination of a DDL Data Definition Language and a DML Data Manipulation Language The query part of the language is similar to SQL The following command answers the query What country arranged the World Cup 1982 AMOS 17 gt select x from Charstring x Country c Tournament t where x name c and c host t and year t 1982 An AMOSQL expression can be entered in one or several lines The commands in AMOSQL are always terminated with semicolon Notice that one difference to SQL is that the FROM clause contains type declarations not table names as in SQL The above query does not utilize the possibilities in AMOSQL to compose functions The following command is equivalent to the previous one AMOS 18 gt select name host t from Tournament t where year t 1982 The commands 17 and 18 actually answer the query What name did the country have that arranged the World Cup 1982 If you really want to retrieve the country object not its name the command would be AMOS 19 gt select host t from Tournament t where year t 1982 Notice here how the system returns object identifiers OIDs for the country objects rather than their names The fol
14. p g 0g AMOS 52 gt create function goals Player p Match m gt Integer g as select g from Integer og where player_participations m p g og AMOS 53 gt create function own_goals Player p Match m gt Integer og as select og from Integer g where player_participations m p g 0g Notice here that the derived functions participating_players goals and own_goals return sets bags of result values and therefore should have the result type Bag of However derived functions always return bags and the Bag of declaration is therefore implicit for derived functions We store new data in the database and make some queries AMOS 54 gt create Match refereed_by played_in spectators instances m1 r1 t12 44000 AMOS 55 gt add player_participations m1 p1 1 0 AMOS 56 gt add player_participations m1 p2 1 0 AMOS 57 gt add player_participations m1 p3 3 0 A A MOS 58 gt name participating_players m1 MOS 59 gt select goals p m1 from Player p where name p Falcao The relationship Teams participate in games and make a number of goals in them is implemented accordingly The participation of teams in games is stored in the function team_participation The two most interesting functions are What teams participate in a certain match and How many goals did a certain team make in a certain match They are defined as derived functions AMOS 60 gt create function team_par
15. s2 wc dmp 4 Types functions and objects The three basic concepts in AMOS II are types functions and objects For those who are used to the terminology used with object oriented programming languages these concepts approximately corre spond to classes methods and instances Types are used for classifying objects Each object is an instance of a type All properties of an object as well as relationships between objects are represented by functions 4 1 Types Entity types in an ER schema corresponds to types in AMOS II We create types for the entity types Country and Tournament see Figure 1 with the following AMOSQL commands AMOS 1 gt create type Tournament AMOS 2 gt create type Country Notice that names of types are case insensitive Internally the system always stores the names of types in upper case However by convention we always capitalize types in this tutorial 4 2 Functions The properties of objects and the relationships between objects are modeled as functions In our exam ple the entity type Tournament has one attribute year We model this as a function year that has a Tour nament as its argument and returns an integer AMOS 3 gt create function year Tournament gt Integer as stored As for type names function names are case insensitive in Amos II and they are internally upper cased In this tutorial we always write function names in lower case In the same way the attribute name of the entity type Countr
16. ses we can use lt rather than The comparison function lt can be used for comparing any kind of object and it thus can order any objects AMOS 83 gt create function goals Match m gt Integer as select goals tl m goals t2 m from Team tl Team t2 where tl lt t2 AMOS 84 gt goals m1 We can now specify the original query AMOS 85 gt select m from Match m where goals m maxagg select goals m1 from Match m1 The answer is not very informative We therefore define the function matchinfo that given a certain match returns a tuple of each participating team how many goals the team made and what year the match was played Then we ask the query once more AMOS 86 gt create function matchinfo Match m gt Charstring n1 Integer g1 Charstring n2 Integer g2 Integer y as select name represents tl goals tl m name represents t2 goals t2 m year played_in m from Team tl Team t2 where participating_teams m t1 and participating _teams m t2 and tl lt t2 AMOS 87 gt select matchinfo m from Match m 15 5 where goals m maxagg select goals m1 from Match m1 In what matches were more than ten goals made AMOS 88 gt select matchinfo m from Match m where goals m gt 10 10 Exercises If you typed something illegal or if there is some error you can recreate the saved correct database with the OS command amos2 wc dmp In Table 1 there is an overview of the
17. te AMOS 76 gt select year t from Tournament t where name represents participating_teams t Sweden 2 How many games have been played by Sweden AMOS 77 gt count select m from Match m where name represents participating_teams m Sweden 14 3 What is the total number of goals made by Sweden AMOS 78 gt sum select goals t m from Team t Match m where name represents t Sweden 4 In what games were most goals made A good start is to define a derived function goals that returns the total number of goals in a match We make a first attempt AMOS 79 gt create function goals 1 Match m gt Integer as select goals tl m goals t2 m from Team tl Team t2 AMOS 80 gt goals1 m1 In the match m Italy made three goals and Brazil two The answer to the query thus ought to be 5 As the function is currently define t and 2 can also be bound to the same team and therefore the erro neous answers 4 and 6 are returned Thus we have to specify that and 72 are different teams AMOS 81 gt create function goals2 Match m gt Integer as select goals tl m goals t2 m from Team tl Team t2 where t1 t2 AMOS 82 gt goals2 m1 The function is no longer returning illegal answers but instead it returns the correct answer twice In one case ft is bound to Italy and 2 to Brazil In the other case 2 is bound to Italy and t to Brazil To only use one of these ca
18. ted twice How many players are members of several teams Types Functions Tournament year Tournament gt Integer host Tournament gt Country participating_teams Tournament gt Team Country name Country gt Charstring Person name Person gt Charstring Referee subtype of Person Player subtype of Person goals Player Match gt Integer 16 Types Functions own_goals Player Match gt Integer Team represents Team gt Country players Team gt Player goals Team Match gt Integer Match refereed_by Match gt Referee played_in Match gt Tournament spectators Match gt Integer player_participations Match gt Player Integer goals Integer own_goals participating_players Match gt Player team_participations Match gt Team Integer goals participating_teams Match m gt Team goals Match gt Integer matchinfo Match gt Charstring c1 Integer g1 Charstring c2 Integer g2 Integer y Table 1 Type and function definitions 11 Referenses 1 D H Fishman et al Overview of the Iris DBMS Object Oriented Concepts Databases and Applications W Kim F H Lochovsky eds ACM Press Addison Wesley 1989 2 Tore Risch Vanja Josifovski Timour Katchaounov AMOS II Concepts http user it uu se torer publ FuncMedPaper pdf 3 Staffan Flodin Martin Hansson Vanja Josifovski Timour Katchaouno
19. ticipations Match gt Bag of Team t Integer goals as stored AMOS 61 gt create function participating_teams Match m gt Team t as select t from Integer g where team_participations m t g AMOS 62 gt create function goals Team t Match m gt Integer g as select g where team_participations m t g 7 7 Aggregate functions Aggregate functions compute aggregate values over bags sum returns the sum of a number of values count counts the number of values maxagg returns the highest value minagg returns the lowest value 12 some equivalent with count gt 0O but much faster notany equivalent with count O but much faster Aggregate functions have somewhat different semantics compared to ordinary AMOS II functions in that they are not applied on each element of a bag as regular functions but on entire bags Consider the query What players participated in the tournament t 2 AMOS 63 gt players participating teams t12 The function participating_teams is applied on the object t 2 With the data stored in the database at this point participating_teams returns two objects bra82 and ita82 Then the function players is applied on each one of the two objects returned from the call participating_teams bra82 and ita82 players bra amp 2 returns two objects p and p2 play ers ita82 returns a single object p3 Thus the result of the complete AMOS
20. tionship is many to many i e a player can play in several teams and a team has several players The function definition therefore becomes AMOS 45 gt create function players Team gt Bag of Player as stored AMOS 46 gt add players bra82 p1 AMOS 47 gt add players bra82 p2 AMOS 48 gt add players ita82 p3 AMOS 49 gt name players bra82 7 5 Functions returning tuples 10 All functions so far have had a single result type It is also possible to have functions that return tuples of values In command 25 the names of persons were defined by the function create function name Person gt Charstring as stored Another possibility could have been to separate the first and family names by defining a function that returns a tuple of two strings create function name2 Person gt Charstring Charstring as stored A person can then be assigned a name with the command set name2 p1 Pavel Smerdjakov Functions for retrieving the first and family names respectively can then be defined as derived func tions calling name2 create function first_name Person p gt Charstring f as select f from Charstring 1 where name2 p f 1 create function last_name Person p gt Charstring as select 1 from Charstring f where name2 p f 1 7 6 and so the final function definitions Now only two relationships from Figure 1 remain to be represented as functions participating_players between Player
21. traints When a stored function is defined AMOS II by default assumes that the function returns one value while the same result can be returned for different values of the argument i e many one relationships For example for the function spectators Match gt Integer command 68 it holds that one match can have one number as the number of spectators while several games can have the same number of spec tators Such constraints on the cardinality of function results or arguments are called cardinality con straints We model the relationship participating_teams between the entity types Team and Tournament as a function from tournaments to teams create function participating_teams Tournament to gt Team tm as stored In a tournament usually more than one team is participating Therefore participating_teams is an example of a function that should return a set of more than one value However the stored function definition above does not allow this To allow participating_teams to return a set of values you can specify Bag of Team as result type create function participating teams Tournament to gt Bag of Team tm as stored When you define the value of a stored function as Bag of the function will represent a many many relationship However the function participating_teams actually represents a one many relationship For a certain value of the input parameter several values are returned there are several teams participating in
22. types and functions that are defined 1 10 11 Make a derived function ref_name Match gt Charstring that given a certain match returns the name of the referee that refereed the match Then use the derived function to answer query 2 Which years were World Cup tournaments played A team is trained by a trainer A trainer has a name and a salary Create the types and functions needed to model this Create a trainer object too Store name and salary for the created trainer Specify thereafter an AMOSQL command showing the name and salary for all trainers Who were the referees in the games where Tomas Brolin played Create a derived function referees Charstring gt Charstring that given the name of a certain player returns the names of the referees that refereed games where that player participated Then use the derived function to answer query 6 How many times did Mexico arrange the World Cup What match had the most spectators Assign the environment variable m to the answer Then use m to retrieve the number of spectators and what teams that played in that match use the function matchinfo What games did Sweden win How many goals did Kurt Hamrin make Create a function that returns the matches in which a given team was playing Create another function computing the total number of goals for a given team Use the function to compute the name of the country in the database making most goals Why is the result repea
23. v Tore Risch and Martin Sk ld Amos IT Release 10 User s Manual http user it uu se udbl amos doc amos_users_guide html 17
24. y becomes a function from countries to strings AMOS 4 gt create function name Country gt Charstring as stored Between the entity types Tournament and Country there is the relationship host This is modeled by a function from tournaments to countries AMOS 5 gt create function host Tournament gt Country as stored The above functions are defined as stored functions as stored This means that the relationship between the argument and the result will be explicitly stored in the database analogous to a table in a relational database There are four kinds of functions in AMOS II In addition to stored functions there are derived functions foreign functions and stored procedures Derived functions are introduced in Section 7 1 Foreign functions are defined in a conventional programming language usually Java For eign functions are not discussed in this tutorial Stored procedures are functions having side effects such as updating the database Stored procedures are not covered by this tutorial Types in AMOS II can be built in or user defined Examples of built in types are Integer Charstring and Real User defined functions are defined with the create type statement e g create type Person Stored functions for a user defined type can be created together with the type definition The com mands 1 5 are equivalent to these commands create type Country properties name Charstring create type Tournament properties
25. yer name instances p1 Falcao p2 Socrates p3 Paolo Rossi Then ask the following query and contemplate the answer AMOS 29 gt select name p from Person p We now create the remaining types from Figure 1 AMOS 30 gt create type Team AMOS 31 gt create type Match 7 More about functions 7 1 Derived functions A function can be defined in term of other functions as a query Such a function is called a derived function For example if we often need to find out the name of the host country for a given year we can define a derived function host_name for this AMOS 32 gt create function host_name Integer y gt Charstring hn as select name host t from Tournament t where year t y AMOS 33 gt select host_name 1982 AMOS 34 gt select host_name 1990 When a query consists of a single function call as the queries 33 and 34 the select can be omitted The queries 33 and 34 can thus also be written as host_name 1982 host_name 1990 7 2 Inverse function definitions Consider the information that countries have names in the EER schema of Figure 1 represented as an attribute name of the entity type Country We represent this as in command 4 i e as a function from countries to names create function name Country gt Charstring as stored The database is then populated with the commands set name ita Italy set name bra Brazil set name esp Spain To get the nam
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