A comment on the last post

Richard Cyganiak Says: May 19th, 2007 at 7:55 pm e
Thanks for this nice introduction Peter. Note that the DBpedia URIs also work in a web browser, so you can go to http://dbpedia.org/resource/Uppsala and the DBpedia server will generate a web page showing the information it has about the item.

I have been playing some more with dbpedia and RDF. (It is important to realise that – as in the above example – many of the accesses will be through UIs, not raw RDF, so casual readers shouldn’t worry). There have been several ways of expressing RDF and these are slightly confusing but the important thing is to know what the predicates and potential values are. The exploratory approach (using a browser) Richard suggests is useful.
Let’s look at chemistry. Assume we know every little about dbpedia but we’ll look at some chemistry. So access Arsenic in Wikipedia

Arsenic

From Wikipedia, the free encyclopedia

Categories: Articles with unsourced statements since February 2007 | All articles with unsourced statements | Metalloids | Pnictogens | Toxicology | Chemical elements | Arsenic

PMR> Note that these Categories will be reusable in RDF triples.

33 germanium ← arsenic → selenium P ↑ As ↓ Sb Periodic Table – Extended Periodic Table
General
Name, Symbol, Number	arsenic, As, 33
Chemical series	metalloids
Group, Period, Block	15, 4, p
Appearance	metallic gray
Standard atomic weight	74.92160(2)  g·mol−1
Electron configuration	[Ar] 3d10 4s2 4p3
Electrons per shell	2, 8, 18, 5
Physical properties
Phase	solid
Density (near r.t.)	5.727  g·cm−3
Liquid density at m.p.	5.22  g·cm−3
Melting point	1090 K (817 °C, 1503 °F)
Boiling point	subl. 887 K (614 °C, 1137 °F)
Critical temperature	1673 K
Heat of fusion	(gray) 24.44  kJ·mol−1
Heat of vaporization	? 34.76  kJ·mol−1
Heat capacity	(25 °C) 24.64  J·mol−1·K−1
P(Pa) 1 10 100 1 k 10 k 100 k
Atomic properties
Crystal structure	rhombohedral
Oxidation states	±3, 5 (mildly acidic oxide)
Electronegativity	2.18 (Pauling scale)
Ionization energies (more)	1st:  947.0  kJ·mol−1
	2nd:  1798  kJ·mol−1
	3rd:  2735  kJ·mol−1
Atomic radius	115  pm
Atomic radius (calc.)	114  pm
Covalent radius	119  pm
Van der Waals radius	185 pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	(20 °C) 333 n Ω·m
Thermal conductivity	(300 K) 50.2  W·m−1·K−1
Young’s modulus	8  GPa
Bulk modulus	22  GPa
Mohs hardness	3.5
Brinell hardness	1440  MPa
CAS registry number	7440-38-2
Selected isotopes
iso NA half-life DM DE (MeV) DP 73As syn 80.3 d ε – 73Ge γ 0.05D, 0.01D, e – 74As syn 17.78 d ε – 74Ge β+ 0.941 74Ge γ 0.595, 0.634 – β– 1.35, 0.717 74Se 75As 100% As is stable with 42 neutrons
References

Arsenic (IPA: /ˈɑːsənɪk/, /ˈɑɹsənɪk/) is a chemical element that has the symbol As and atomic number 33. Its Atomic Mass is 74.92. Its Ionic Charge is (3-) Its position in the periodic table is shown at right. This is a notoriously poisonous metalloid that has many allotropic forms: yellow (molecular non-metallic) and several black and gray forms (metalloids) are a few that are seen. Three metalloidal forms of arsenic with different crystal structures are found free in nature (the minerals arsenic sensu strictu and the much rarer arsenolamprite and pararsenolamprite), but it is more commonly found as arsenide and arsenate compounds. Several hundred such mineral species are known. Arsenic and its compounds are used as pesticides, herbicides, insecticides and various alloys.

The box on the right is the “infobox” and it is many of these properties that find their way into dbpedia. The property names are not yet fully standardised and not all are memorable, but Wikipedian chemists can – and I suspect will – work on these to stnadrdaize. In which case they can be used for RDF/SPARQL queries. For example:
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You can work out some of the property names by comparing against their values. For example…

links to the melting point in degC. There is still some work to be done (e.g. linking properties and units) but RDF is well suited for this and we’ll be working out some approaches.