1 Explicit and Implicit LIST Aggregate Function for Relational Databases Witold Litwin Université Paris 9 Dauphine

2 Summary New Aggregate Function Transforms a set of values into single one –Char type A basic long time need Should be highly useful

3 Plan Motivating Examples Explicit LIST Implicit LIST Conlusion Further Work

4 Motivating Example 1 The Supplier-Part (SP) table of the best- known S-P database

5 Motivating Example 1 The classical query : select SP.[S#], Sum(SP.Qty) AS [Total Qty] from SP group By SP.[S#]; S#Total Qty S11300 S2700 S3200 S4900 How to get also the individual quantities ?

6 Motivating Example 2 A database of persons having: –Multiple Hobbies –Multiple preferred Restaurants –Many Friends Best design: –four 4-NF tables P (SS #, Name), H (SS#, Hobby), R (SS#, Rest), F (SS#, Friend)

7 Database

8 Fragment

9 Query select P.[SS#], P.Name, F.Friend, R.Rest, H.Hobby from ((P INNER JOIN F ON P.[SS#] = F.[SS#]) INNER JOIN H ON P.[SS#] = H.[SS#]) INNER JOIN R ON P.[SS#] = R.[SS#] where P.[SS#] ="ss1" ; Select Name, Friends, Restaurants, Hobbies, of Person SS1 SQL :

10 Result Usable ???

11 General Problem Current RDBs manage tables in 1NF –All attributes are single-valued (atomic values) Example 1 ; We wished –Single-valued attribute : SUM(QTY) –Multi-valued attribute Individual quantities The result would not be 1NF

12 General Problem RDB manages tables in 1NF –All attributes are single-valued Example 2 ; We wished : –Single-valued attributes : S#, Name –Multi-valued attributes (multi-sets): Hobby, Rest, Friend The result is normalized to 1NF –{(ss1,Witold, x, y, z) : x Hobby, y Rest, z Friend } –The table is not in 4NF –Subject to well-known anomalies

13 Solutions Design RDBS for 0NF tables –A revolution –0NF RDBS will not be here for years Aggregate set or multi-set values into atomic values –An evolution –All RDBS already do it using: SUM, AVG, COUNT… perhaps with GROUP BY –We need a new aggregate leaving the entire set visible E.g: (multi)-set of values X => (single) list of values X

14 Local Culinary Example The set-valued attribute: –(Schwarz, Wälder; Kirchen, Chocoladen, Torte) The aggregated attribute: –Schwarzwälderkirchenchocoladentorte Local specialty, try it !

15 Explicit LIST function Select S#, sum (Qty) AS [Total Qty], LIST (Qty) AS Histogram from SP group by S#;

16 Explicit LIST function select P.SS#, Name, LIST (DISTINCT (Friend)), LIST (DISTINCT (Rest)), LIST (DISTINCT (Hobby)) from P, F, R, H where P.SS# = F.SS# and F.SS# = R.SS# and R.SS# = H.SS# and P.SS# ="ss1" group by P.SS#, Name ; P NameFriend RestHobby SS1WitoldAlexis, Christopher, Ron, Jim, Donna, Elisabeth, Dave, Peter, Per-Ake, Thomas Bengal, Cantine Paris 9, Chef Wu, Ferme de Condé, Miyake, Louis XIII, Mela, North Beach Pizza, Pizza Napoli, Sushi Etoile Bike, Classical Music, Good food, Hike, Movie, Science Fiction, Ski, Swim, Tennis, Wine

17 Explicit LIST function Simulated actual output using MsAccess forms with list boxes Form with three subforms No SQL query used

18 Explicit LIST function select P#, SUM (Qty) as [Total Qty], LIST (S#, Qty) as [Per supplier] from SP group by P#; P#Total Qty Per supplier p1600s1 300 s2 300 p21000s1 200 s2 400 s3 200 s4 200 p3400s1 400 p4500s1 200 s4 300 p5500s1 100 s4 400 p6100s1 100

19 Implicit LIST function For any single-valued A : –A = LIST (A) Any non-aggregated attribute in an SQL query has to be in the GROUP BY clause Now, any non-aggregated perhaps composite attribute A from a single table and not in GROUP BY clause is implicitly under –LIST (DISTINCT (A)) Queries may become less procedural

20 Implicit LIST function select P#, SUM (Qty) as [Total Qty], S#, Qty from SP group by P# having S# QTY like *s4*; Implicit LIST is LIST (S#, QTY)

21 Implicit LIST function Query Select S.*, P#, Qty From S, SP Where S.S# = SP.S# Repeats all the data of the supplier S in every resulting tuple –6 times for S1: its Name, City, Status Query Select S.*, P#, Qty From S, SP Where S.S# = SP.S# Group By S.S# Does it only once per supplier Less redundancy

22 Implicit Joins and From Equijoins following the referential semantic links or integrity may be implicit MsAccess, SQL Server… FROM clause content can be inferred from the attribute names Even less procedural formulation may result: select P.SS#, Name, Friend, Rest, Hobby group by P.SS#, Name ;

23 Implementation Issues Should be easy for the RDBS owner –Any RDB already processes the aggregates Already done hiding the list Should also be shown

24 Implementation Issues For explicit LIST, foreign function interface may suffice –Oracle, DB2, Yukon… –See related work in the paper for current (limited) proposals Oracle & iAnywhere (core code) Not for the implicit LIST –Access to core code is necessary

25 Conclusion LIST is a new aggregate function Aggregates a multi-valued attribute into a single value Responds to a long-standing fundamental RDBS user need - 30 years ? Should be rather easy to implement Future work should start with the implementation –Using foreign functions for explicit LIST

26 Research Support European Commission ICONS Project –no. IST Microsoft Research

27 Thank You for Your Attention Witold Litwin Université Paris 9 Dauphine