Month: April 2011
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Something more on Fibonacci numbers
My earlier blog about the Fibonacci series gets a lot of hits, so I thought I would write something more, as clearly there is interest. Once again this is from “Structure and Interpretation of Computer Programs” (available for free here electronically): Let and . Then . So . (1) (2) Then (3) Simplifying (2) (4) […]
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Ubuntu 11.04 now on the install phase
Took all night to download the upgrade files and now on to the installation. Have switched browsers to Google Chrome as it’s a third party app and won’t be touched by the update process.
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Cyclic Redundancy Checks
If you have ever downloaded any software from the internet you are quite likely to have seen a reference to a “CRC” – a cyclic redundancy check. I have been reading about them as I plough on through Andrew Tanenbaum‘s (pictured) Computer Networks: so here is an explanation based closely on his text (though it’s […]
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Ubuntu 11.04 upgrade
This is now under-way on the machine I am typing this on – but the servers are plainly congested as I getting about 45kB/s download speeds – so it won’t be finished until some time tomorrow morning.
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Do universities fail science students?
There is a very interesting article on the THES website today – “So last century” – which says that universities are failing students because they teach them in such a compartmentalised way. Whether the study is conducted by the CBI in the UK or by commercial for-profit educational providers drumming up business for their remedial […]
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Looks like a great book
My copy of C. J. Date‘s SQL and Relational Theory: How to Write Accurate SQL Code turned up today – I have only read one chapter so far but already I have a feeling that it is going to have been worth every penny. Date is concerned not to write another SQL primer but to […]
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Relational division again
Take the same relational database tables as before: RESTAURANT(RT_ID, NAME, TYPE, LOCATION) PROXIMITY(RT1_ID, RT2_ID, DISTANCE) USER(U_ID, NAME, EMAIL) REVIEW(U_ID, RT_ID, RT_DATE, RATING, COMMENT) Find the names of the reviewers who reviewed all the restaurants in Earlsfield. In relational algebra: But what about SQL? As I wrote of relational division when I started the blog: one […]
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Relational algebra problem
Have a relational database with the following tables RESTAURANT(RT_ID, NAME, TYPE, LOCATION) PROXIMITY(RT1_ID, RT2_ID, DISTANCE) USER(U_ID, NAME, EMAIL) REVIEW(U_ID, RT_ID, RT_DATE, RATING, COMMENT) What’s the relational algebra for “name of any user who has never given Chez Brian a rating lower than 5”? Is this right? Related Articles CoSQL: SQL and noSQL are really just […]
cartesian product ... stuff about computing mostly 