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Newsgroups: comp.databases.theory
From: mikl...@gmail.com
Date: 18 Sep 2006 11:57:27 -0700
Local: Mon, Sep 18 2006 8:57 pm
Subject: Ternary Relationship cardinality
Hi,
I am working on an assignment which has 2 ternary relationship. I'm Maybe I am going through one of those mental blocks... Can someone give me some cardinality examples for N-ary relationships? My other option is to convert the 3-ary relationship into a weak Is it ok to have N'ary Relationships which includes recursion? looks Thanks, Mike You must Sign in before you can post messages.
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Newsgroups: comp.databases.theory
From: J M Davitt <jdav...@aeneas.net>
Date: Tue, 19 Sep 2006 00:00:30 GMT
Local: Tues, Sep 19 2006 2:00 am
Subject: Re: Ternary Relationship cardinality
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Newsgroups: comp.databases.theory
From: mikl...@gmail.com
Date: 18 Sep 2006 23:57:19 -0700
Local: Tues, Sep 19 2006 8:57 am
Subject: Re: Ternary Relationship cardinality
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Newsgroups: comp.databases.theory
From: Jonathan Leffler <jleff...@earthlink.net>
Date: Tue, 19 Sep 2006 07:10:11 GMT
Local: Tues, Sep 19 2006 9:10 am
Subject: Re: Ternary Relationship cardinality
mikl...@gmail.com wrote: Cardinality = number of { rows, records, tuples } in a relation. > I am working on an assignment which has 2 ternary relationship. I'm > can't figure out their cardinality. > Maybe I am going through one of those mental blocks... > Can someone give me some cardinality examples for N-ary relationships? Count the number of 'rows' in the table - that's the cardinality. Degree = number of { fields, columns, attributes }. Ternary relations have degree 3 (or 'are of degree 3'). > My other option is to convert the 3-ary relationship into a weak You may also lose marks for misspelling 'lose' (and not using plurals, > entity.. but I'll definitely loose marks on that and using "I'm can't" for "I can't", etc). > [...] -- You must Sign in before you can post messages.
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Newsgroups: comp.databases.theory
From: mikl...@gmail.com
Date: 19 Sep 2006 01:03:22 -0700
Local: Tues, Sep 19 2006 10:03 am
Subject: Re: Ternary Relationship cardinality
I know what cardinality is... and I know how to implement it
My problem is with the notation for a particular Ternary relationship. (Supertype) [Parent]------[0..*]----- <Breeding> The prob is when I use the N:1 notation..my first reaction would be to (Supertype) [Parent]------1----- However that doesn't make sense since ParentA can be related to Many PS I'm using Chen notation You must Sign in before you can post messages.
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Newsgroups: comp.databases.theory
From: "Jan Hidders" <hidd...@gmail.com>
Date: 19 Sep 2006 01:41:29 -0700
Local: Tues, Sep 19 2006 10:41 am
Subject: Re: Ternary Relationship cardinality
mikl...@gmail.com wrote: Your ASCII art is a bit unclear so let me tell you how I interpret > I know what cardinality is... and I know how to implement it > My problem is with the notation for a particular Ternary relationship. > (Supertype) [Parent]------[0..*]----- <Breeding> this: - You have a relationship Breeding(Parent1, Parent2, Child) Your depicted cardinality constraints are as follows: - Each Child participates in exactly one instance of that relationship. - Each Parent participates in zero or more instances of that Minor detail: if *every* child has two parents your database will > The prob is when I use the N:1 notation..my first reaction would be to The general rule is as follows: If you have a relationship R(a,b,c) > do something like this: > (Supertype) [Parent]------1----- then you have to ask for each role, say 'a', how its cardinality depends on the combination of the other two, in this case 'b' and 'c'. If the upperbound is 1 then you put 1 on the corresponding edge in the diagram, if there is no upperbound you put N or M there. So let's look at Child. Given two particular parents what is the upper Clear? -- Jan Hidders You must Sign in before you can post messages.
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Newsgroups: comp.databases.theory
From: mikl...@gmail.com
Date: 19 Sep 2006 02:42:24 -0700
Local: Tues, Sep 19 2006 11:42 am
Subject: Re: Ternary Relationship cardinality
Hi Jan,
> The general rule is as follows: If you have a relationship R(a,b,c) Thanks for the insight... > then you have to ask for each role, say 'a', how its cardinality > depends on the combination of the other two, in this case 'b' and 'c'. > If the upperbound is 1 then you put 1 on the corresponding edge in the > diagram, if there is no upperbound you put N or M there. > Minor detail: if *every* child has two parents your database will Care to expand on this? Note that parents can come into existence by > either be infinite or some will be their own descendants. purchase, however since Children are a specialization of 'parent', they can also breed. Thanks, Mike You must Sign in before you can post messages.
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Newsgroups: comp.databases.theory
From: "Jan Hidders" <hidd...@gmail.com>
Date: 19 Sep 2006 02:54:59 -0700
Local: Tues, Sep 19 2006 11:54 am
Subject: Re: Ternary Relationship cardinality
Ah, wait, now I understand your sub/superclass annotation. You say that
Child is a subclass of Parent (btw. letting both be a subclass of Dog or whatever might be more logical) and a dog is in the class Child iff it has parents.In that case there is no problem. -- Jan Hidders You must Sign in before you can post messages.
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Newsgroups: comp.databases.theory
From: mikl...@gmail.com
Date: 19 Sep 2006 03:22:04 -0700
Local: Tues, Sep 19 2006 12:22 pm
Subject: Re: Ternary Relationship cardinality
> Ah, wait, now I understand your sub/superclass annotation. You say that I don't think I can generalize both in 1 class... the actual heirarchy > Child is a subclass of Parent (btw. letting both be a subclass of Dog > or whatever might be more logical) and a dog is in the class Child iff > it has parents.In that case there is no problem. is abit more complex than the parent/child example. Person Not using the actual names as they got us all paranoid about this Thanks Again, Mike You must Sign in before you can post messages.
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Newsgroups: comp.databases.theory
From: "Jan Hidders" <hidd...@gmail.com>
Date: 19 Sep 2006 04:47:15 -0700
Local: Tues, Sep 19 2006 1:47 pm
Subject: Re: Ternary Relationship cardinality
mikl...@gmail.com wrote: It depends a bit on which ER dialect you happen to be using. Strictly > > Ah, wait, now I understand your sub/superclass annotation. You say that > > Child is a subclass of Parent (btw. letting both be a subclass of Dog > > or whatever might be more logical) and a dog is in the class Child iff > > it has parents.In that case there is no problem. > I don't think I can generalize both in 1 class... the actual heirarchy > Person speaking, if you specify that A IS-A C and B IS-A C this only means that every A is a C, and every B is a C. So it does not mean that A and B are disjoint (i.e., there can be entities in both A and B) or that every C is either an A or a B. Usually there are special combined isa-edges to denote the latter two constraints. But, again, this may depend on the dialect your instructor / professor is using, so be sure to check the IS-A semantics in the notation you have to use. -- Jan Hidders You must Sign in before you can post messages.
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