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Re: why hierarchy?

From: Neo <neo55592_at_hotmail.com>
Date: 26 Jul 2006 09:02:35 -0700
Message-ID: <1153929755.298416.183230@75g2000cwc.googlegroups.com>

> > example/ex007.asp
>
> One hiearchy is talking about ancestors of persons, the other about origins of persons. The hierarchies record the persons twice.

I can't speak for other methodologies, but dbd doesn't record things redundantly in the db, regardless of how many hierarchies they are in.

> Relations would record them once and record ancestors once and record origins once.

True, if the proper schema is used.

> Many problems with hierarchies - here's one: if a user is aware of only one hierarchy and discovers that there is no such person as John and 'deletes' him, the other hierarchy is now wrong, as is the DB.

I can't speak for other methodologies, but this problem does not occur in dbd as things are only represented once, even if they are in multiple hierarchies. Deleting John deletes him from both hierarchies in db.

> > To verify which method's underlying data model is more general, one can observe the impact on existing schema/data/query when meeting future unknown data requirements (to be proposed by someone else). Would someone be willing to engage in this trivial example?
>
> It does seem trivial.

Could you post the script for the initial data/queries so that we can observe the impact on them when meeting future unknown data requirements (to be proposed by someone else)? The more general methodology will be impacted the least. Below is dbd's script. Lines starting with "(;" are comments.

(; Create a class directory item and name it age)
(new)
(create clsDir item (it))
(create (it) name (word+ 'age))

(; Create a main directory item and name it god)
(new)
(create dir item (it))
(create (it) name (word+ 'god))

(; Create a class directory item and name it person)
(new)
(create clsDir item (it))
(create (it) name (word+ 'person))

(; Create a person named adam)
(new)
(create person instance (it))
(create (it) name (word+ 'adam))

(; Create a person named eve)
(new)
(create person instance (it))
(create (it) name (word+ 'eve))

(; Create a person named john whose age is 35)
(new)
(create person instance (it))
(create (it) name (word+ 'john))
(create (it) age (val+ '35))

(; Create a person named mary whose age is 25)
(new)
(create person instance (it))
(create (it) name (word+ 'mary))
(create (it) age (val+ '25))

(; Create god's children hierarchy)
(; Note: verbs parent/child are system verbs)
(createWRR god child adam)
(createWRR god child eve)
(createWRR adam child john)
(createWRR adam child mary)
(createWRR eve child john)
(createWRR eve child mary)

(; Create a main directory item and name it universe)
(new)
(create dir item (it))
(create (it) name (word+ 'universe))

(; Create a class directory item and name it planet)
(new)
(create clsDir item (it))
(create (it) name (word+ 'planet))

(; Create planet mars)
(new)
(create planet instance (it))
(create (it) name (word+ 'mars))

(; Create planet venus)
(new)
(create planet instance (it))
(create (it) name (word+ 'venus))

(; Create universe's part hierarchy)
(; Note: verbs asm/part are system things)
(createWRR universe part mars)
(createWRR universe part venus)
(createWRR mars part john)
(createWRR venus part mary)

(; Find eve's children)
(; Finds john and mary)
(select eve child *)

(; Find john's parents)
(; Finds adam and eve)
(select john parent *)

(; Find adam's children that are part of mars)
(; Finds john)
(and (select adam child *)

     (select mars part *))

(; Find eve's children that are part of a planet)
(; Finds john and mary)
(and (select eve child *)

     (select (select planet instance *) part *))

(; Find god's grandchildren that are part of a planet)
(; Finds john and mary)
(; Note: they are found twice since each has two parents)
(and (select (select god child *) child *)

     (select (select planet instance *) part *)) Received on Wed Jul 26 2006 - 11:02:35 CDT

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