Wikipedia:Reference desk/Archives/Computing/2013 April 29

= April 29 =

wifi problems
I have Comcast cable internet and the cable modem has a built-in wifi router. The wifi used to work fine, but now it often can't connect with some but not all of the computers in the house. With the Dell laptop I'm using (Windows XP) the router shows up very strong when scanning for signal, but connection fails. After a few hours it will sometimes connect and then work great for several hours before failing the same way. With a Lenovo computer it works solidly but an Ipad apparently doesn't find the signal at all. The hardware diagnostic on the Dell says everything is working. Any idea what's going on? 98.207.66.10 (talk) 00:36, 29 April 2013 (UTC)
 * Those problems are suggestive of RF interference issues. Unfortunately there are a lot of possible causes, but the first question would be whether anything has been added to your environment that generates radio waves.  (If not, it could be coming from a neighboring house.)  You might read this article for background. Looie496 (talk) 16:01, 29 April 2013 (UTC)
 * Is there a microwave oven on, or a bluetooth device (these both run at the same frequency as WiFi). Is there another WiFi access point using the same channel number as your point (I know how to check in Linux for this, but never done it in MS-Windows). CS Miller (talk) 21:27, 30 April 2013 (UTC)

Max CD-RW size
What is the maximum size for reinscriptibles CD.

I know there are 900Mb CD-R, but I can't find the same size for CD-RW.2A02:8422:1191:6E00:56E6:FCFF:FEDB:2BBA (talk) 10:26, 29 April 2013 (UTC)


 * The maximum size should be the same. The difference between CD-R and CD-RW disks is just in what materials are used to make the data layer.  That said, the higher capacities of writeable CD work by violating the standard in ways that most (but not all) drives can deal with, and the lower contrast of CD-RW as compared to CD-R could reduce compatibility too much at the higher densities. --Carnildo (talk) 03:10, 1 May 2013 (UTC)
 * There are no standard violations (like overburning), the standard has been updated recently. 900Mo can be read on any drive, You just need a writer that support it.
 * I often burn live CDs but, since the new standard most linux distributions seems to consider you have the largest size (900M).It is interesting to update the CD with newer iso rather than keeping all version.
 * My writer can't erase DVD-RW so this the reason of the question.2A02:8422:1191:6E00:56E6:FCFF:FEDB:2BBA (talk) 13:35, 1 May 2013 (UTC)

Group website
I'm trying to find a website or similar service I can create a group on for a club I'm part of, somewhere people can talk and post information on upcoming events and things like that, a sort of social networking place. I'd want something quick and easy for people to sign up to, too. I've considered facebook, google+ and skype, but none of them are quite what we want

anyone know of anything like this?

213.104.128.16 (talk) 15:22, 29 April 2013 (UTC)


 * How about phpBB?--Shantavira|feed me 07:31, 30 April 2013 (UTC)


 * Hmm, maybe. I like forums, but they don't do real-time chat, which maybe we could manage without, and there's too much emphasis on lists of comments, rather than the other aspects, personal profiles, event planning and calendars, noticeboards and useful things like that. unless, I can get those added and/or made more noticeable and useful by the way I configure the basic layout of the site? 213.104.128.16 (talk) 10:05, 30 April 2013 (UTC)

Nintendo DS/3DS Connectivity
Hey, guys. It's bugging me not to know this, so here goes. Say you have a Nintendo DS with a DS game loaded. You can normally wirelessly connect to another DS (for example trading Pokemon in the 4th or 5th generation games), BUT... is it possible between a DS and a 3DS, or two 3DS' with original DS paks loaded? Prompt answer, please. --JadeGuardian (talk) 17:38, 29 April 2013 (UTC)
 * I think you are talking about protocols
 * it is possible in Wi-fi but what make think that nintendo don't use a custom protocol beetween their consoles2A02:8422:1191:6E00:56E6:FCFF:FEDB:2BBA (talk) 19:43, 29 April 2013 (UTC)
 * I can say that yes, the two devices can connect to each other for certain. I do it all the time.  Mingmingla (talk) 21:42, 29 April 2013 (UTC)


 * I believe it has something to do with how the 3DS runs in "DS mode" when you have an original game pak loaded (correct me if I'm wrong, I don't remember where I read this so don't quote me on it!) but regardless you should have no troubles communicating between the chips. --Yellow1996 (talk) 01:25, 30 April 2013 (UTC)

strong and weak entity sets
I'm currently reading "Database System Concepts" by Silberschatz-Korth-Sudarshan. I was going through the section describing the strong and weak entity sets in an ER model. Here's the section. An entity set may not have sufficient attributes to form a primary key. Such an entity set is termed a weak entity set. An entity set that has a primary key is termed a strong entity set. As an illustration, consider the entity set payment, which has the three attributes: payment-number, payment-date, and payment-amount. Payment numbers are typically sequential numbers, starting from 1, generated separately for each loan. Thus, although each payment entity is distinct, payments for different loans may share the same payment number. Thus, this entity set does not have a primary key; it is a weak entity set. For a weak entity set to be meaningful, it must be associated with another entity set, called the identifying or owner entity set. Every weak entity must be associated with an identifying entity; that is, the weak entity set is said to be existence dependent on the identifying entity set. The identifying entity set is said to own the weak entity set that it identifies. The relationship associating the weak entity set with the identifying entity set is called the identifying relationship. The identifying relationship is many to one from the weak entity set to the identifying entity set, and the participation of the weak entity set in the relationship is total. In our example, the identifying entity set for payment is loan, and a relationship loan-payment that associates payment entities with their corresponding loan entities is the identifying relationship. Although a weak entity set does not have a primary key, we nevertheless need a means of distinguishing among all those entities in the weak entity set that depend on one particular strong entity. The discriminator of a weak entity set is a set of attributes that allows this distinction to be made. For example, the discriminator of the weak entity set payment is the attribute payment-number, since, for each loan, a payment number uniquely identifies one single payment for that loan. The discriminator of a weak entity set is also called the partial key of the entity set.

First, it was mentioned that the attribute payment_number can be the same for different loans, so, the entity set is weak. Then again, it's said that the attribute has unique values for the same loan. So, it can act as a discriminator. Why in one case, different loans are taken, while in the other, the same loan? In simpler words, why are not, in both cases, either multiple loans taken, or a single loan taken? — Preceding unsigned comment added by 117.197.254.199 (talk) 18:16, 29 April 2013 (UTC)


 * I can't really make sense of your question. In the first place, the sentence "the attribute has unique values for the same loan" is nonsense, and the passage you quoted doesn't say it.  In the second place, I don't understand what the word "taken" is supposed to mean when applied to a loan.  Let me try, though, to clarify the passage as I understand it.  Suppose we have two loans:  loan 1 is to Smith, loan 2 is to Jones.  Both of those loans have a payment numbered 12.  The attribute loan-number is not a primary key because if I simply refer to payment 12, you can't tell which loan is being referred to.  However, within the context of the loan to Smith, knowing that the payment number is 12 is sufficient to tell me exactly which element of the database is being referred to. Looie496 (talk) 22:18, 29 April 2013 (UTC)


 * Perhaps it would help to give some examples of table layouts. Here's one way:

LOAN_PAYMENTS ============= *Loan number *Payment number Payment date Payment amount


 * In this case, the combination of Loan number and Payment number is needed to form a unique key. Presumably another table would exist describing attributes of the loan, as follows:

LOAN_DETAILS ============ *Loan number Loan amount Loan period Loan origination date Loan interest rate Loaner Loanee
 * For an alternate example, let's now suppose that you own a small business which only has two loans they've taken out. While the following approach isn't optimal, in that it doesn't scale up nicely when the business grows and has many loans, many might set it up as a table for each loan anyhow:

RIPOFF_BANK_PAYMENTS ==================== *Payment number Payment date Payment amount

REPO_BANK_PAYMENTS ================== *Payment number Payment date Payment amount


 * In this case, the payment number alone is a unique key, within each table. StuRat (talk) 19:34, 1 May 2013 (UTC)