Re: Argument for 1NF by counter-example

From: Neo <neo55592_at_hotmail.com>
Date: 31 Oct 2004 19:05:45 -0800
Message-ID: <4b45d3ad.0410311905.759ab576_at_posting.google.com>

>>> If it can query relational db's that contain hierarchical data
>>> then people would start to use it.
>>> 
>> Could you give a small example of hierarchal data/query that is
>> difficult in RM that people would like XML/XQuery to solve?
>>
> Probably anything that the SQL "WITH RECURSE" clause provides, the ability
> to walk a hierarchy and produce a flattened relation.  The employee
> organizational chart is as good a common example as any.

While XDb2 is neither RM or XML/XQuery, below is an example of creating/walking an employee hierarchy. Each person is given a simple name that reflects his level in the hierarchy to make it easier to follow however a person's name could be anything. Note that person z has several bosses.

a
 a1
   a1a
   a1b
   z
 a2
   a2a
   a2b

      z
 a3
   z

// Below script represents the above things/hierarchy

CREATE2 *person.cls = thing;
CREATE2 *a.cls = person;
CREATE2 *a1.cls = person;
CREATE2 *a1a.cls = person;
CREATE2 *a1b.cls = person;
CREATE2 *a2.cls = person;
CREATE2 *a2a.cls = person;
CREATE2 *a2b.cls = person;
CREATE2 *a3.cls = person;
CREATE2 *a3a.cls = person;
CREATE2 *z.cls = person;

// Create verbs to relate persons

CREATE2 *boss.cls = verb;
CREATE2 boss.vbType = kr; // boss leads to higher level in hier CREATE2 *employee.cls = verb;
CREATE2 employee.vbType = cr; // employee leads to lower level in hier CREATE2 boss.opposite = employee;

// Create hierarchy

CREATE2 a.employee = a1;

CREATE2 a1.employee = a1a;
CREATE2 a1.employee = a1b;
CREATE2 a1.employee = z;

CREATE2 a.employee = a2;
CREATE2 a2.employee = a2a;
CREATE2 a2.employee = a2b;
CREATE2 a2b.employee = z;
CREATE2 a.employee = a3;
CREATE2 a3.employee = z;

// Select a's immediate employees

SELECT2 a.employee = %;

// Select a's employees and their employees recursively
SELECTR a.employee;

// Select a's distinct employees recursively
// Note: Distinct works if a is root of employee hierarchy
SELECTRD a.employee;

// Select z's bosses recursively

SELECTR z.boss;

// SELECTR and SELECTRD call function T_Relative()
// which is exposed via API

 while(x = T_Relative(pAThing, pVerb, distinct_b){    // do stuff
 } Received on Mon Nov 01 2004 - 04:05:45 CET