Re: Trying to define Surrogates

JOG wrote:

> [apologies for the cross posting].
>
> Bob Badour wrote:
>

>>I disagree that the concept of surrogate vs. natural is useful.

>>It is a surrogate for whatever a surrogate key is for. Think of any
>>natural key. How is it not a surrogate?

>>My name is not me. It is an arbitrary identifier chosen by my parents.
>>It is familiar because I was conditioned from an early age to respond to it.

I respectfully suggest that no important distinction exists between a label and a surrogate as used in the context of candidate keys.

>>My SSN is not me. It is an arbitrary identifier chosen by the IRS to
>>identify tax filings related to my income. It is familiar because I was
>>given a little blue card with it inscribed, and I was instructed to
>>transcribe it to a variety of documents.

>>[snip]
>>I am not suitably represented for machine processing.

And when we use the values of labels to identify the values of the labels, no surrogacy is required. When we use the labels to identify me, they stand as surrogates for me.

Candidate keys are labels. Values are self-identifying and self-labelling.

> However, there are some identifiers that we do not have suitably
> formatted labels for. Attributes that are currently not easy to enter
> into a proposition. Fingerprints for example.

Does it matter whether the fingerprint has been scanned and digitized and represented suitably for machine processing?

  Some attributes might not
> be easily recordable even though we know they exist. These are
> attributes not suitable for machine processing.

Define 'easily'. Fingerprints are recorded. Genomes are recorded. Feature-length films are recorded. CT scans are recorded. What is too difficult to record? The exact location and velocity of a sub-atomic particle? The only reason we cannot record that is we cannot measure it in the first place.

> Hence we 'subsitute' that key with a different artificial key we have
> generated, to act as its representative. That is what surrogacy is.

How exactly does that differ from labelling? We have a fingerprint and we label it 'Defense Exhibit 117' or we label it 532673294. We then use the label to refer to the fingerprint.

This is merely case of trading off simplicity and familiarity.

> The blur comes in that this is only really useful at design time,
> because as soon as the attribute is used externally, it becomes a new
> natural key. Hence I agree that after the fact the distinction is not
> useful, but a priori it is important to /understand/ exactly what's
> going on as it eliminates any foolhardy temptation to try and hide such
> attributes and violate the information principle.

I suggest it is more illuminating to /understand/ during design that one is making a pragmatic design tradeoff among a handful of sometimes conflicting design criteria: simplicity, familiarity, stability, irreducibility.

If one remembers that familiarity is a design criterion and why it is a design criterion, one won't feel any temptation to hide anything. Received on Thu Aug 17 2006 - 16:38:38 CEST