Steve Mallett has paid me a huge compliment calling my site the "closest DataLibre site I've seen" although I'm somewhat embarrassed because I'm still a long way from where I want to be.
I'm still thrilled Steve likes where I'm going, though. DataLibre is one the two main drivers (the other being REST) in how I'm implementing Leonardo. In fact, I'm considering describing Leonardo as "a RESTful DataLibre server written in Python".
I received my November copy of HBR today and there was a Forethought article entitled "I Am My Own Database" by Richard T. Watson which is pretty much talking about DataLibre. He describes what is referred to in the article as "customer-managed interaction" or CMI:
Under CMI, when a consumer buys merchandise online, he receives an electronic file that describes his purchases and that can be automatically imported into a database he's installed on his home PC. If he wants to record purchases made earlier or offline, the consumer can obtain an electronic list of common products, like books, and CDs, from the Library of Congress or commercial sources such as the Internet service Gracenote. He also registers an opinion of each purchase by using rating software incorporated into the database. The database remains in the consumer's control at all times, so if he decides that the Led Zeppelin period of his life has irretrievably passed, he can simply change his ratings of Led Zeppelin CDs he's purchased from all sources.
Finally, while writing this entry, it occurred to me that readers of the datalibre-discuss mailing list might be interested in the Forethought article. In true DataLibre fashion, I'll post this entry (along with the permalink) to the list. One feature I want to implement in Leonardo is that kind of "trackback to an email address" feature.
by : Created on Nov. 17, 2004 : Last modified Feb. 8, 2005 : (permalink)
Imagine a school dance. There is a set of boys and a set of girls. When the music starts, each boy picks a girl to dance with.
Think of this as a mapping from a boy to a girl, or from an element in the set of boys to an element in the set of girls.
The mapping is said to be injective (or one-to-one) if each boy picks a different girl. If two boys try to dance with the same girl, the mapping isn't injective.
The mapping is said to be surjective (or onto) if no girls are left without a partner. If there is a girl not dancing, the mapping isn't surjective.
If the mapping is both injective and surjective it is said to be bijective.
You can immediately tell if there are the same number of boys and girls if the mapping is bijective—in other words, each boy is dancing with one and only one girl and no girls are left without a boy to dance with.
The existence of a bijection can be used to demonstrate that two sets have same number of elements or, in the case of infinite sets, have the same cardinality.
Bijections are also very important in establishing the equivalence between two structured sets (for example between two topological spaces) as we shall see in the near future.
UPDATE: next post
by : Created on Nov. 17, 2004 : Last modified Feb. 8, 2005 : (permalink)