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Primer review, part 2: Basic Notions

From: Alan Ruttenberg <alanruttenberg@gmail.com>
Date: Mon, 21 Jan 2008 03:00:22 -0500
Message-Id: <3BAEE089-0002-467F-9AAC-990217627E74@gmail.com>
To: OWL Working Group WG <public-owl-wg@w3.org>

These comments are on the Primer document http://webont.org/owl/ 
documents/primer.html as accessed late night 1/20/2007. They are  
detailed comments on Section 3: Basic Notions..

Comments below are intended to be in order of presentation in the  
document. Both major and minor comments are included. To make things  
clear, I write this not from the point of view of chair, but from the  
point of view of OWL practitioner and educator.

General: I wonder about using manchester syntax absent a complete  
reference to the syntax.

----

"OWL allows us to express information about the world then to draw  
certain consequences based on this information. There are OWL tools -  
reasoners - that can automatically compute these consequences. "

+ or answer queries that depend on them.

-----

"As IRIs are long, we will use a compact way of writing them in OWL,  
consisting of a prefix and a reference separated by a colon."

"reference"?

----

easier for non-logicians to read

->

easier to read

----

easier for reasoning tools to use

->

easier for tools that manipulate owl to use

(like editors)

----

General: First paragraph italicizes names of new things. Second  
paragraph doesn't, e.g "Functional-Style syntax", "OWL XML syntax",  
"Manchester syntax", are, in effect, new technical terms and of the  
same kind as "individuals", "objects" in the previous paragraph.  
There are a variety of places through the document where such new  
terms could be profitably called out typographically, making it  
easier to scan for definitions.

----

"(Currently some examples only have the Manchester syntax. "

probably worth having a typeset distinction between editorial  
comments and text of the document.

----

"Suppose we want to represent information about a particular family.  
We first need to determine what individuals there are in a family,  
and how they are related to each other and what data values are  
associated with them. We can then proceed by writing down all this  
information in OWL."

->

"Suppose we want to represent information about a particular family  
in OWL. We first identify the individuals in the family, how they are  
related to each other and what data values are associated with each.  
Once we've done this analysis, we can start writing this information  
using OWL."

-----

"So if we have a family with parents John and Mary and children Susan  
and Bill we could write all this down, along with ages as follows."

"If our family is made of up four individuals, parents John and Mary  
and their children Susan and Bill, and we want to associated an age  
with each,  we would write this down as follows."

----

"primer uses four different syntaxes, by default the Manchester  
syntax is the only one shown; the buttons below can be used to show  
or hide all three syntaxes"

four/three nonagreement

----

s/hasAge/isAge/ so it reads more closely like english. Also keeps  
perspective consistent. A record has an age field, but a person  
doesn't "have" an age.

Perhaps unnecessary, but contributes to rigor - the age is in years -  
no mention of units.

----

Visual presentation.
- Too much space between lines in manchester syntax. Can control with  
css.
- f: prefix everywhere makes it hard to read. Perhaps use gray font,  
or offer to get rid of them. An interesting switch might be to expand  
all IRIs to their full form. Might be useful to have the first  
example show the full form, in any case, to compare. Cssing the  
syntax elements would let us play with that presentation.
- RDF/XML syntax could use entities &f; &xsd; etc. so it is easier to  
read, analogous to using f:
- Diagrams are easier to understand than text to a certain class of  
reader. Might be worth augmenting with diagrams to also cover them.
----

ex.com -> example.com (common idiom - perhaps even recommended?)  
googlefight

----

"We could also write down information about the sex of people by  
providing them with a gender, which is either male or female"

Got to this part and first comment to mind was "Better to include  
this in the analysis at the top then to introduce it mid way."

Then realized that this was to be the way the section was developed.

Maybe start  the section with something like: In this section we will  
represent information about a particular family. We'll start with  
[...] and then successively record more information as we proceed.

----

It might be nice to demonstrate best practices and include  
rdfs:comments with definitions for classes and properties before  
using them.

----

"However, all we have done so far is written down the basic facts  
about a particular family. Although OWL can be used for this purpose,  
it is not OWL's forté. OWL's main strength here, instead, involves  
how families work in general."

I don't think I would bother saying this.

----

(This is the process of knowledge representation. Like all processes  
representing information about the world, certain simplifying  
assumptions must be made, and since this is a primer we are going to  
be simplifying a lot.)

Again, necessary?

----

"class of people, with name Person"

->

class of people, which we will name "Person"

----

"wife is a relationship between Persons"

Do you mean hasWife ?

same issue with age/hasAge and throughout with other properties.

----

"domain and range"

italicize, as they are new terms. Possibly include text explaining  
what they mean.

----

"From this information we can conclude that John belongs to Person,  
because, for example, the domain of wife is Person and John has a  
wife. We can also directly state that an individual belongs to a class."

While true, I think more explanation is need explaining that this is  
how domain and range work, and contrasting this with the constraint  
view of the world. RDFS people, may have confusingly read the Primer,  
which says:

"RDF Schema, on the other hand, provides schema information as  
additional descriptions of resources, but does not prescribe how  
these descriptions should be used by an application. For example,  
suppose an RDF schema states that an ex:author property has an  
rdfs:range of class ex:Person. This is simply an RDF statement that  
RDF statements containing ex:author properties have instances of  
ex:Person as objects.

This schema-supplied information might be used in different ways. One  
application might interpret this statement as specifying part of a  
template for RDF data it is creating, and use it to ensure that any  
ex:author property has a value of the indicated (ex:Person) class.  
That is, this application interprets the schema description as a  
constraint in the same way that a programming language might.  
However, another application might interpret this statement as  
providing additional information about data it is receiving,  
information which may not be provided explicitly in the original data."

----

3.2 Information about Properties
starting "There is more that can be said even..."

I wonder here whether the explanations should be more interwoven with  
the syntax. There's a lot to absorb in this one paragraph and it  
might be difficult for the novice to connect what is said to the  
particular expression.

----

"Complete OWL reasoning tools can efficiently determine whether a  
particular consequence follows from the information available"

perhaps here and elsewhere say something more from the point of view  
of the user. To exaggerate: What do I care about what the tool can  
do. I want to know what I can do.

----

3.3 Information About Classes

How to connect "saying that every Person that has gender male belongs  
to man" with "EquivalentTo:"

needs something explicit.

Or perhaps, here, and elsewhere use annotations to include the  
comment with the formal statement.

----

"Complete definitions enable many consequences in OWL"

Haven't introduced "Complete" anywhere - only "every xxx that xxxx  
belongs to xxxx", and EquivalentTo:

-----

"It may seem that there is a circularity in defining Parent as people  
with at least one child and also making it be the domain of child. In  
OWL, however, there is no problem. The two bits of information are  
simply different ways of saying the same thing."

They don't say the same thing.  "similar things"?

-----

"we might have Teenager" -> "we might define Teenager"

----

"Child as those people whose age is in the complement of adult ages"

true, but language not friendly for beginners. Might be better to  
expand a bit and introduce "complement" and relate it to "not".

----

"From this, Bill belongs to Teenager, but not Adult. Both John and  
Mary belong to Adult, but not to Teenage. Mary belongs to neither  
Adult nor to Teenage."

might want, for emphasis, to include the statement that the reasoner  
would derive:

e.g. Bill type teenager. Mary type not (Adult or Teenage).

----

"This would provide exactly the same information to OWL"

->

"This would provide exactly the same information to an OWL reasoner"

or

"In OWL, this expresses the same information".



Alan
Received on Monday, 21 January 2008 08:00:39 GMT

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