It collects instances of relations as input and gives occurrences of relations as output. The general case of JOIN operation is called a Theta join. presides over the trial for defendant known as Mike starting on Relational Algebra is a system used to model data stored in relational databases. Are there conventions to indicate a new item in a list? Project: Famous people. Joining three tables can be as easy as joining two tables. Difference between Relational Algebra and Relational Calculus. Joining tables to themselves with self-joins. can the natural-join be seen as a subset of the equi-join and theta-join? RV coach and starter batteries connect negative to chassis; how does energy from either batteries' + terminal know which battery to flow back to? My relational algebra query is like this, am I right ? JOIN operation also allows joining variously related tuples from different relations. This essentially means that both relations have the exact same attributes. | solutionspile.com We perform a join whenever multiple tables appear in the FROM clause of the query. Note that while writing a JOIN clause, we arent limited to the columns in the SELECT clause we have access to all the columns! In the right outer join, operation allows keeping all tuple in the right relation. How can I list the tables in a SQLite database file that was opened with ATTACH? What tool to use for the online analogue of "writing lecture notes on a blackboard"? SQL Relational algebra query operations are performed recursively on a relation. But before we analyze an example query for this technique, lets check the last table in our schema. There are two obvious ones: student and course. The image down below shows a small database. Left outer join = natural join + mismatch / extra tuple of R1. This time, well use the teacher table. @rd_nielsen right I see that they all have some form of team ID, but how do you form the statement that tells you if you should be using the home team or the guest team's ID. If youd like to read more about LEFT JOINs, check out How to LEFT JOIN Multiple Tables in SQL on LearnSQL.com. Relational Algebra is a procedural query language, which takes Relation as input and generates relation as output. Not the answer you're looking for? First, lets introduce a few tables. {xy| dij0C|SArIRj-sRC9$?M6jf0EM3EQ%o TL? The first step is to look at the schema and select the columns we want to show. We will see in the next section, about Joins, that once we take a cross product with a condition, we can start to gather meaningful data from this. Challenge: Sequels in SQL. 3. some of its concepts are incorporated into the SQL standard query language for RDBMSs. Output Selects tuples from Tutorials where the topic is Database and author is guru99. Have you ever wondered how to join three tables in SQL? True An outer join is basically of three types: Left outer join. Relational databases store tabular data represented as relations. Each row of the table represents a single instance of the relation, or, in OOP terms, an object of that class. To learn more, see our tips on writing great answers. The relationship between the student and course tables is called a many-to-many relationship. Then, were joining it with the student_course table and, finally, with the course table. The projection method defines a relation that contains a vertical subset of Relation. Two approaches to join three or more tables:1. In contrast, we do have to join DEFENDANT with TRIAL: a DEFENDANT 's primary key is his ID, so only that ID appears in the TRIAL table, so if we need to select a defendant by name, we have to employ a join. It uses various operations to perform this action. Notice how Jname is the primary key of JUDGEs, that is to say, a judge is uniquely identified by her name; and the TRIAL table will actually contain Jname denoting which judge presided over a given trial: You can see how selecting tuples yields us the judge's name without joining anything in. Given below are a few examples of a database and a few queries based on that. a. This operation also relies on the two tables being union compatible. The above result should clearly show what to do next. xM,7GL" f9W?H]# @q/n{U={zzq];n.?\0{[R.]O?~{aopbE]NreE?"]N2e(S. (I removed the student_course.id column, as we wont need it.) endobj How to react to a students panic attack in an oral exam? Joins operation in Relational Algebra. Join operation in relational algebra is a combination of a Cartesian product followed by which satisfy certain condition. The principle of SQL JOIN is based on the relational algebra operation of the same name - a combination of Cartesian product and selection. The union of the two will be the required answer. endobj Weve already seen the usage of the junction table. As for your question title: yes, you can of course join more than three tables. PS. SQL Relational algebra query operations are performed recursively on a relation. K^\,\(- +UHp6\4.H].W|D1HW. SQL Joins, Relational operators, Relational Algebraic expressions, Query evaluation, Access time, matching records, Result set. 4. See examples of when to use which. Purchases table contains eid referencing employees and pid referencing products. What are the capabilities of DBMS and why relational DBMS is powerful. In a full outer join, all tuples from both relations are included in the result, irrespective of the matching condition. The best way to practice SQL JOINs is LearnSQL.com's interactive SQL JOINs course. endstream rev2023.3.1.43269. 542), How Intuit democratizes AI development across teams through reusability, We've added a "Necessary cookies only" option to the cookie consent popup. R and S must be the same number of attributes. The database now has the following three schemas: Team (teamid,teamname,stadium) Player (playerid,name,teamid, height) Game (gameid, hometeamid, guestteamid, date, home-score, guest-score) I am a little confused on how to do this since the tables that I seem to need do not have anything in common (Game and Team). If we take the cross product of this table with Person, we end up with a new table of 5 columns, with each row getting a distinct combination of the tuples from both rows. How did StorageTek STC 4305 use backing HDDs? What is a SQL self join and how does it work? (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(hs); The attribute name of A has to match with the attribute name in B. UNION is symbolized by symbol. Technology and Mathematics : Calculus 1-3, Linear Algebra, Data Structures, Algorithms, Regular Expressions, Requirements Analysis, Python, Java (Programming Languages), MySQL (Relational . Relations in relational algebra are seen as sets of tuples, so we can use basic set operations. J HJ'! If perform natural join on this table and Person, we will end up with a result of the Person table, along with the corresponding location at which their favorite food is obtained from. <> While joining, you cant use columns from not-yet-introduced tables. Joining 3 Tables Using a Junction Table Step 1 The first step is to look at the schema and select the columns we want to show. We have students connected with the IDs of the courses theyre taking. Create column X as primary key in one table and as foreign key in another table (i.e creating a parent-child relationship).Lets look in the tables created:s_id is the primary key in student table and is foreign key in marks table. Making statements based on opinion; back them up with references or personal experience. Tables stored in relational database and their Step 1: Create tables. [WV$3\pFE-9W$a".mpm[CP:P("]p# JFIF XICC_PROFILE HLino mntrRGB XYZ 1 acspMSFT IEC sRGB -HP cprt P 3desc lwtpt bkpt rXYZ gXYZ , bXYZ @ dmnd T pdmdd vued L view $lumi meas $tech 0 rTRC. We just have to use the JOIN clause one more time. Clash between mismath's \C and babel with russian. To learn more, see our tips on writing great answers. If youve just learnt JOINs in SQL, you might think that its limited to two tables. The name and type of the attribute must be same. What is the difference between UNION and UNION ALL? r stands for relation which is the name of the table. It includes all tuples that are in tables A or in B. Last time we put the student table in the FROM clause. Whereas the algebra defines a set of operations for the relational model, the relational calculus provides a higher-level declarative language for specifying relational queries. Lets study various types of Inner Joins: The general case of JOIN operation is called a Theta join. This query is pretty similar to the previous one. R1 R2 with condition R1.regno > R2.regno. Asking for help, clarification, or responding to other answers. Do EMC test houses typically accept copper foil in EUT? })(); How To Join 3 Tables In Relational Algebra, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window). It also eliminates duplicate tuples. Inner Join is further divided into three subtypes: 1) Theta join 2) Natural join 3) EQUI join Theta Join allows you to merge two tables based on the condition represented by theta stream meredith48034 meredith48034 Answer: the sum of 4 and a number 4 plus a number New questions in Mathematics To find the price, a monopolist looks at the price _____ at the chosen quantity. (A table can also be called a relation, although relational "purists" would argue that there is a subtle distinction between the two. Find centralized, trusted content and collaborate around the technologies you use most. Inner joins are of two types - Theta Join and Equi Join. Together with the example of the cross product. Using JOIN in SQL doesnt mean you can only join two tables. Take a look at the first two rows in the student_course table. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. A relation is usually described as a table, which is organized into rows and columns. Additionally, a row can be represented as a tuple, which is simply a comma delimited list of all attributes in the row enclosed in parenthesis. The first one won't work, though. It uses operators to perform queries. Core Relational Algebra Union, intersection, and difference. You will learn how to left join 3 tables in SQL while avoiding common mistakes in joining multiple tables. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. many rows with the same student_id can be in the table student_course) and one course can be attended by many students (i.e. (function() { SELECT E.Lname, E.Salary, M.Lname, M.Salary Find centralized, trusted content and collaborate around the technologies you use most. When we have two relations that have a single column (lets just call this column C) in common, we can perform what is known as a natural join. Finally, looking at the course table, we can read that English literature and Python programming have IDs equal to 2 and 3, respectively. For example, theres a reference between the student and student_course tables each student can be linked to multiple rows in the student_course table. Computer Science questions and answers. I did some editing. Explain the select operation in relational algebra (DBMS)? Copyright - Guru99 2023 Privacy Policy|Affiliate Disclaimer|ToS, DBMS Keys: Candidate, Super, Primary, Foreign Key Types with Example, Functional Dependency in DBMS: What is, Types and Examples, DBMS Joins: Inner, THETA, Outer, Equi Types of Join Operations, 55 Best MS Access Courses & Training Classes Online (2023), The SELECT operation is used for selecting a subset of the tuples according to a given selection condition. Will this relational algebra statement return my expectation, Relational algebra statement to eliminate duplicates, Relational algebra natural join of table q2 with rename of table q2 for Passenger-Flight-Trip, Find all pizzerias that serve ONLY pizzas eaten by people over 30. How do you translate this English statement into Relational Algebra? In an outer join, along with tuples that satisfy the matching criteria, we also include some or all tuples that do not match the criteria. There are many versions of "relational algebra". Determine the name and the department number of the employees that are engineers and have salary greater than 2000. However, what you really want is all the. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It is denoted by symbol . Write expression of relational algebra using Employee table shown in slide 3. a. By the way, why we have to do the cross product because relation algebra of SQL is important to function has joined. This way, we introduce each table before using it in a JOIN ON condition. SQL Server | Convert tables in T-SQL into XML, SQL - SELECT from Multiple Tables with MS SQL Server, Copy tables between databases in SQL Server using Import-and-Export Wizard, Insert multiple values into multiple tables using a single statement in SQL Server, Compare and Find Differences Between Two Tables in SQL, Select into and temporary tables in MS SQL Server, Copy tables between databases in SQL Server. stream Projective representations of the Lorentz group can't occur in QFT! endstream First, we select the columns: teacher.first_name, teacher.last_name, student.first_name, and student.last_name. many rows in the table student_course can have the same course_id). In contrast, we do have to join DEFENDANT with TRIAL: a DEFENDANT's primary key is his ID, so only that ID appears in the TRIAL table, so if we need to select a defendant by name, we have to employ a join. <> var hs = document.createElement('script'); hs.type = 'text/javascript'; hs.async = true; endobj What factors changed the Ukrainians' belief in the possibility of a full-scale invasion between Dec 2021 and Feb 2022? %PDF-1.4 The mismatching values of R2 are filled with NULL. ***** Go to Relational Algebra Operations page. If you dont know this term, I recommend checking out An Illustrated Guide to the SQL Non-Equi Join on the LearnSQL.com blog. Relational Query Optimization Jianlin Feng School of Software SUN YAT-SEN UNIVERSITY courtesy of Joe Hellerstein for some slides Review Choice of single-table operations Depends on indexes, memory, stats, Joins Blocked nested loops: simple, exploits extra memory Indexed nested loops: best if 1 rel small and one indexed Sort/Merge Join good with small amount of memory, bad with duplicates . Not the answer you're looking for? Think of the EMPLOYEE table as two tables, one for employees and one for managers. stream Notify me of follow-up comments by email. How did StorageTek STC 4305 use backing HDDs? 185 endobj Products and joins: compositions of relations. Learning JOINs With Real World SQL Examples. If we join R1 and R2 on equal condition then it is called natural join or equi join. How can I change a sentence based upon input to a command? Meanwhile, take a look at the example data from these three tables: Its important to notice that the student_course table is a junction table. If you find it hard to imagine, recall that R S T = (R S) T. Note that natural join is nicely commutative and associative as well. Examples included! acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structure & Algorithm-Self Paced(C++/JAVA), Android App Development with Kotlin(Live), Full Stack Development with React & Node JS(Live), GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, How to make a website using WordPress (Part 2), How to make a website using WordPress (Part 1), Step by Step guide to Write your own WordPress Template, Step by step guide to make your first WordPress Plugin, Making your WordPress Website More Secure, Basic SQL Injection and Mitigation with Example, SQL | DDL, DQL, DML, DCL and TCL Commands, SQL | Join (Inner, Left, Right and Full Joins), How to find Nth highest salary from a table. It's easy when you know the basics. Multiple database tables in the relational database model can be queried using SQL-JOINs. Thanks for contributing an answer to Stack Overflow! The mismatching values of R1 are filled with NULL. 3 0 obj The truth is that you can easily extend this idea to three tables or even more. 5 0 obj Using joins in sql to join the table:The same logic is applied which is done to join 2 tables i.e. + :nT7-zI?NR_c R'Yz,Ma`fU=sswsM_ Renaming of relations and attributes. Building queries with Relational Algebra. In this example, weve analyzed how to write a query with equi JOINs were using equality in our joining conditions. Cartesian ( or sometimes, Cross) Product: This operation does not need the two tables being operated on to be union compatible. Essentially two tables are naturally joined by taking the cross product of the two tables, then eliminating all combinations in which the column C from table 1 and column C from table 2 are not equal. Instead of using my own example, the Wiki article actually has a very simple example. An operator can be either unary or binary. The relational algebra is often considered to be an integral part of the . Union: A union of two relations (R1 U R2) can only be performed if the two relations are union compatible. Relational Algebra Introduction. This way, we can show the first and last name of each student together with the courses theyre attending. Join operation is essentially a cartesian product followed by a selection criterion. 8 0 obj Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The open-source game engine youve been waiting for: Godot (Ep. For example, Shreya Bain (the student with id = 1) is connected to English literature (the course with id = 2) and Python programming (the course with id = 3). An Illustrated Guide to the SQL Self Join. Excel Pivot Table Sort Dates By Month And Year, Pivot Table Not Showing Dates Only Months Into Week, Pivot Table Not Showing Dates Only Months Into Days, Pivot Table Not Showing Dates Only Months Into Year, Pivot Table Group Dates By Month In Filtered Range Or, Pivot Table Group Dates By Month In Filtered Dataframe, Pivot Table Group Dates By Month In Filtered Data Excel, Pivot Table Group Dates By Month In Filter Data, Pivot Table Group Dates By Month In Filtered Ranges, Pivot Table Group Dates By Month In Filter Range, Deck Bearer And Joist Span Tables Australia, Birmingham Arena Seating Plan With Seat Numbers, Glycemic Load Chart Fruits And Vegetables, Cutter Sanborn Three Figure Author Table Pdf, Supplier Contact Tables In Oracle Apps R12. Left outer join: Left outer join contains the set of tuples of all combinations in R and S that are equal on their common attribute names. It uses various operations to perform this action. It contains over 90 hands-on exercises that let you refresh your SQL JOINs knowledge. Making statements based on opinion; back them up with references or personal experience. This operation joins two tables based on a condition that is defined when declaring the join. However, well have to find a way to join these tables. Explain the evaluation of relational algebra expression(DBMS). { we select those tuples from cartesian product where R1.regno=R2.regno}. Fear not well explain it thoroughly in the next section. \|!(RErk#csM Just dont forget about the semicolon at the end of your code. Theta join in relational algebra, theta join in relational model, theta join relational algebra query and its equivalent SQL queries, binary theta join operation in relational algebra . It's important to use table names when listing your columns. RELATIONAL ALGEBRA is a widely used procedural query language. The relational algebra calculator was created by Johannes Kessler BSc at Databases and Information Systems Group at the Institute of Computer Science at the University of Innsbruck under supervision of Michael Tschuggnall PhD and Prof. Dr. Gnther Specht External resources Natural join can only be performed if there is a common attribute (column) between the relations. Can I use a vintage derailleur adapter claw on a modern derailleur, The number of distinct words in a sentence, Rename .gz files according to names in separate txt-file. Conclusion. What is the "N+1 selects problem" in ORM (Object-Relational Mapping)? <> Joining two additional tables is nearly the same as the process we used earlier. Challenge: Customer's orders. In fact, you can join as many tables as you like the idea behind it is the same as joining only two tables. Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? A Relation can be thought of as a class in traditional OOP programming. Find all tables containing column with specified name - MS SQL Server. The join yields a table with attributes: Employee.Name, Employee.Id, Employee.Salary, MngrId Manager.Name, Manager.Id, Manager.Salary. Relational algebra mainly provides a theoretical foundation for relational databases and SQL. Study with Quizlet and memorize flashcards containing terms like The order of the rows and columns is important to the DBMS., In a natural join, the column on which the join was made occurs twice in the new table., Relational algebra defines the theoretical way of manipulating table contents using relational operators. endobj In a full outer join, all tuples from both relations are included in the result irrespective of the matching condition. Connect and share knowledge within a single location that is structured and easy to search. Example Queries on Relational Algebra. So We need to 2 tables R1 and R2 both two relation table (R1 R2 ). I've three tables , employees, purchases and products. What's the difference between a power rail and a signal line? Natural join can only be performed if there is a common attribute (column) between the relations. <> Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Lorentz group ca n't occur in QFT before we analyze an example for... Select operation in relational databases that are in tables a or in B 2 tables R1 and on... The online analogue of `` relational algebra is a system used to model data stored in relational databases and.. Example, the Wiki article actually has a very simple example can use set... The natural-join be seen as sets of tuples, so we can use basic set operations into and... Types of Inner JOINs: the general case of join operation is a. You translate this English statement into relational algebra join 3 tables algebra is a combination of a database and author is guru99 equi.. And SQL ever wondered how to left join multiple tables appear in result... An oral exam also allows joining variously related tuples from Tutorials where the topic database..., Employee.Salary, MngrId Manager.Name, Manager.Id, Manager.Salary equi-join and theta-join are compatible... Joining two tables being operated on to be union compatible use the join clause one more time attributes... User contributions licensed under CC BY-SA other answers 's the difference between a power rail and few... Do they have to follow a government line as sets relational algebra join 3 tables tuples, we! In EU decisions or do they have to use the join clause more. Examples of a cartesian product where R1.regno=R2.regno }, finally, with same! Technologies you use most Mike starting on relational algebra '' tables is nearly the same as process! Sqlite database file that was opened with ATTACH to join three tables or even.. The department number of the equi-join and theta-join in joining multiple tables mainly a... Using my own example, the Wiki article actually has a very simple example students attack! Analogue of `` relational algebra is a widely used procedural query language, which takes relation input... Defines a relation SQL Server column ) between the student and student_course tables each student can be by! Or sometimes, cross ) product: this operation JOINs two tables based on that same.... A query with equi JOINs were using equality in our joining conditions 3 tables in SQL doesnt mean you easily. Of each relational algebra join 3 tables together with the student_course table step is to look at the end of your code right... Weve already seen the usage of the Lorentz group ca n't occur in QFT ( )... You agree to our terms of service, privacy policy and cookie policy the! Filled with NULL relation table ( R1 U R2 ) are included in the relational algebra (. On opinion ; back them up with references or personal experience the query for this technique lets! # csM just dont forget about the semicolon at the first two rows in right. Within a single location that is defined when declaring the join clause one more time single location that is and. Course_Id ) relation as output the relational algebra is a system used to model data stored relational! To learn more, see our tips on writing great answers in OOP terms, an of! Two relations ( R1 R2 ) can only be performed if there a! The natural-join be seen as sets of tuples, so we can show the first step to., matching records, result set table names when listing your columns be to! Join on the relational database model can be thought of as a table with:! Between union and union all, teacher.last_name, student.first_name, and student.last_name selection... Student_Course ) and one course can be queried using SQL-JOINs of attributes as easy as joining two... Non-Equi join on the LearnSQL.com blog columns from not-yet-introduced tables as easy joining... Of `` writing lecture notes on a relation can be as easy as joining two being! To use table names when listing your columns they have to do cross... S orders usage of the Employee table as two tables being operated on to be union compatible multiple. With russian how does it work to practice SQL JOINs knowledge students connected with the courses theyre taking foil... Containing column with specified name - MS SQL Server as for your question title:,. More time were using equality in our schema as you like the idea behind it called! Table as two tables operation of the relation, or, in OOP,! In ORM ( Object-Relational Mapping ) only join two tables as a subset of relation easily this... Removed the student_course.id column, as we wont need it. is the name and the department number the. Dbms and why relational DBMS is powerful and collaborate around the technologies you use most * Go relational... Relations are included in the student_course table algebra is often considered to be an integral part of the employees are! Under CC BY-SA language for RDBMSs a power rail and a few examples of a database and a queries! A sentence based upon input to a command * * * * * * * Go relational., theres a reference between the student and course tables in SQL doesnt mean you can as! Access time, matching records, result set then it is called natural join mismatch... Name of each student can be attended by many students ( i.e of R2 are filled with.! Full outer join, all tuples from cartesian product and selection of Inner JOINs are of two types Theta... Using join in SQL a system used to model data stored in relational database model can be to. Recommend checking out an Illustrated Guide to the SQL Non-Equi join on the LearnSQL.com blog multiple tables in! + mismatch / extra tuple of R1 idea behind it is called a Theta and! Of its concepts are incorporated into the SQL Non-Equi join on the LearnSQL.com blog be to! Certain condition by clicking Post your answer, you might think that its limited to two tables being operated to... Many versions of `` writing lecture notes on a blackboard '' relation can be in the student_course table that relations. Many students ( i.e R2 ) user contributions licensed under CC BY-SA generates relation as output few examples of cartesian! Relational Algebraic expressions, query evaluation, Access time, matching records, result.. You can only be performed if there is a SQL self join how. We used earlier many rows in the right outer join is based on the two tables, one managers... Or responding to other answers the cross product because relation algebra of SQL is. While joining, you agree to our terms of service, privacy policy and cookie.! Described as a subset of the table represents a single location that is when... Object-Relational Mapping ) references or personal experience columns: teacher.first_name, teacher.last_name, student.first_name, difference... General case of join operation in relational databases and SQL relation table ( R1 R2... The two tables, employees, purchases and products we join R1 and R2 on equal condition then it the... Select operation in relational database and author is guru99 Access time, matching records, result set { dij0C|SArIRj-sRC9. The SQL standard query language, which takes relation as output and one course be... End of your code attack in an oral exam a blackboard '' R2 both two relation table ( R1 R2. Operated on to be an integral part of the query performed recursively on a blackboard '' and... Learn how to vote in EU decisions or do they have to do the cross because! Join can only be relational algebra join 3 tables if there is a SQL self join and equi join can easily extend this to! Selection criterion relation, or, in OOP terms, an object that... All tables containing column with specified name - a combination of cartesian product selection... And attributes allows joining variously related tuples from different relations or responding to other answers > joining two tables. Endobj Weve already seen the usage of the relations in relational algebra ( DBMS ) expressions, evaluation... Is database and their step 1: Create tables this English statement into relational are. One more time easy as joining two additional tables is called a Theta join and how does work... Mngrid Manager.Name, Manager.Id, Manager.Salary the IDs of the query: yes, you cant use columns from tables... Single instance of the table student_course can have the same name - MS SQL Server Illustrated! As joining only two tables to three tables because relation algebra of SQL is important to use join! The IDs of the courses theyre attending and easy to search you will how. Query operations are performed recursively on a blackboard '' with equi JOINs using! This, am I right, why we have to follow a government?! And have salary greater than 2000 knowledge within a single instance of the Employee table two... Queries based on a relation thought of as a subset of relation specified name - MS SQL Server with.. S important to use table names when listing your columns to follow a government line Projective of. Union all a many-to-many relationship a relational algebra join 3 tables attribute ( column ) between the student and course tables is the! New item in a list Mapping ) attributes: Employee.Name, Employee.Id, Employee.Salary, MngrId Manager.Name, Manager.Id Manager.Salary... A Theta join and equi join are a few queries based on opinion back... Join in SQL While avoiding common mistakes in joining multiple tables appear in the next section tool use. Allows joining variously related tuples from both relations have the same name MS! Can use basic set operations name - a combination of cartesian product followed by a selection.... Database model can be in the relational database model can be queried using SQL-JOINs considered to be compatible!