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what is a functiona dependency in data base?
nill
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ok fine, if we talk about the employee number and name, we can write
enumber-> ename is it right. e number is unique, against every unique value of e number there exist a name,
now where functional dependency breaks, we may have more than one value of name ie enumber 12= maria similarly enumber 20 = maria.
is it ename depends on enumber,
nill
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Thanks Grand
ur reply clearify my cocepts, i was clearifying it for a week,
regards.
nill
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can iahe any useful web link to study more about FD. having relations and to fine fd from there. After exercise the answers are also provided.
nill
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i am basically doing my research thesis for MSCS, i was required concept of f.d, keenly studing data mining and a concept of f.d was inta=eracting my area. so i was clearifying it.
nill
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Is there a way to write a generic user interface that can be the base UI for both a web app and a windows app.
I understand that by using a n-tiered architecture you can create one buisiness layer and one data layer for both the Web UI and the Windows UI. Taking this same approach there should be a way to create one UI that can be used through a web browser and through a windows form.
With the WPF and silverlight it seems that both user interfaces (web and windows) could share the same xaml code. The silverlight app would then have Javascript and the Windows app would not.
Any thoughts on the subject would be appreciated.
Patrick McCoy
Developer
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I think that it is possible, however the feature set common to both is so small that no serious app is able to accomplish it readily at the moment.
WPF and WPF/E (I hate the term Silverlight) is a step in the right direction but it's not usable on anything but XP or greater so a big problem for me.
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Browser development is a combination of a garbage dump and a mine field. With that said it is possible to do but at what cost? Depending on the application it could involve additional complexity in exponential proportion yet never quite achieving the possible user experience quality of a desktop application. If you know anything about the history of browser development this problem is self evident.
The first silver bullet was Java. Oh the dreams of rich user interfaces in Java embedded as object tags in HTML. Well we all know what happened with that. Today we have massive amounts of javascript code where the structure of most of it makes the worst C code I have ever seen look about as complex as a rubber duck. And still in most cases it is buggy at best and from a user experience perspective, I just look for the X button and never, NEVER return to that site. If you decide to go down this route be prepared to read the never ending literature on all the silver bullet solutions available while attempting to find those that will fill all your needs.
So for me the bottom line is this. If you want to deliver a low quality user experience and a high budget project go for it, but don't bother asking me to work on it. 
led mike
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Hi Guys,
I have been working with databases in a professional enviroment for about 2 years now. Currently where i work there is a tendancy to encourage flat packed code with inline SQL. My attempt to get them to move over to datasets failed.
I regularly find myself trying to figure out exactly how a complex set of functionalty should be written, and while i use Datasets, i find them to be an irritation for a few reasons:
1) The typed Datatables don't support null types
2) The DataRows don't have a parameterless constructor.
2) I can't throw together an ad-hoc query and get a non schema checked report back.
3) They are pretty bulky.
However, they do make throwing working code together increadably fast, but they aren't the neatest solution in the world.
I also feel there must be a fundamentaly different approach when using databases between a Client based app and a web app. I don't think that a fully functional ORM would be particularly useful in a web enviroment as it's not really nescessary. Many database functions are small and singular with the exception of large scale reports.
I'm basicaly looking for something which covers the following points:
1) Lightewight DataObjects and DataAdapters (Not nescessarily .Net Standard Library)
2) Where the DataObjects have parameterless constructors.
3) Where the DataObjects support nullable types.
4) Where the DataObjects support serialization.
5) Where the DataAdapters support Transactions.
6) Where the DataAdapters Support Multi-Batch Reports (Into a collection of tables or DataObjectArrays)
7) Where the DataAdapters load DbCommand objects on demand, rather than upfront. (TableAdapters currently generate all the DbCommands on Init, even if you are only using one)
8) Some kind of integrated SQL Generator for both Stored Procs and text based SQL.
I've looked at a few ORM tools, but they seem excessively complicated for my needs.
Do people have any thoughts on this, or any pointers?
I like Code and i like Databases, but they seem to have some kind of mental compatibility issue for me.
Cheers
Tris
-- modified at 11:31 Tuesday 8th May, 2007
-------------------------------
Carrier Bags - 21st Century Tumbleweed.
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Tristan Rhodes wrote: but they seem to have some kind of mental compatibility issue for me.
Tristan Rhodes wrote: Do people have any thoughts on this, or any pointers?
Umm ... Get over it.
Tristan Rhodes wrote: I don't think that a fully functional ORM would be particularly useful in a web enviroment as it's not really nescessary.
You need to explain that "not really nescessary" part. Perhaps you have some specific project requirements that indicate that otherwise, in general, I would disagree.
led mike
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led mike wrote: Umm ... Get over it.
Thanks :P
Fair comment tho. My issue is that there are so many ways to use databases, i never know in what way to use them for any given solution.
I guess it comes with experience.
T
-------------------------------
Carrier Bags - 21st Century Tumbleweed.
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Hello experts,
I'm working on a system which would be able to dinamically load all kinds of multiplayer games.
In order for the system to know how to handle any game, I set up some ground rules using an abstract class named GameEngine.
Among other stuff, it contains an abstract ProcessMessage() method.
At first I thought of loading DLLs from a special folder, and analyzing every class which inherits GameEngine.
But then came another thought into my mind...
What if someone, instead of implementing a game, inherits GameEngine and puts down malicious code into ProcessMessage()?
My first solution is not to read DLLs from a directory, but to read only a DLL that I will code... Whenever I want to add another game, I would update the DLL...
However, this prevents other programmers from adding games to my program...
What can I do?
Thanks in advance,
Shy.
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shyagam wrote: What if someone, instead of implementing a game, inherits GameEngine and puts down malicious code
A plugin system is per design an "open system", what means malicious code here?
First of all, the game user needs to download and install a plugin, so I would say if someone uses code from an unknown source he/she is generally responsible for caused damage! In case you just want to protect users from e.g. downloading broken plugins then have a checksum with each DLL that your downloader checks (i.e. SHA1 checksum does no match with DLL then delete it). Perhaps you can offer quality control to plugin developers and give a "verified" rating to decent plugins... or list good plugins on your webpage (e.g. see IrfanView)?
If your question is about limiting plugins from sources other than yourself: You could sign each DLL cryptographically or have an initial handshake with a "license" that enables certain functionality... but at the end of the day this can be technically circumvented since the algorithm/key is somewhere inside the plugin or the application. When I follow the PS/Wii/Xbox modding scene I think vendor locking attempts are quite futile...
Hope it helps.
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Hello,
I am designing a Library Managment system for a school project. It includes 3 main constructs behind the UI:
Member - contains details about a member including a unique ID (using GUID's) and an array of Loan objects.
Book - contains details about a book, a unique ID and a reference to a single Loan object.
Loan - contains due date, issue date, unique ID and references to both the Member and Book which the loan is based upon.
Everything is fine up to here but once it comes to saving/loading this data problems appear. I want to have three seperate files, one which contains all the Books, one containing Members and a third containing all the Loans. Now the obvious way todo this would be to simply save the ID of the object if it is contained in a seperate file so for example the Loan object would be saved containing two GUIDs, one pointing to the Member and one pointing to the Book. That's all fine and dandy but when it comes to loading the files how should I approach creating the individual objects? I don't really want the complications of loading and saving to shine through in my object model as that would be bad design. Any suggestions? I am using C# to build this project by the way.
Thanks,
Daniel
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You've raised some very interesting points, thank you. I have been thinking about this and as you say the Member and Book objects should not really need to be dependant upon the Loan object. I have now revised my object model:
Member - contains information about the member and a unique identifier.
Book - contains info about the book such as Title, ISBN, Author and a unique identifier.
Loan - a relationship between a Member and a Book with due date, issue date, etc.
To me it seems logical to use three seperate files. Why should the Members file have anything to do with the Book file, since they have no direct relationship without a Loan connecting them. Also I am considering using Serialization which would mean rewriting the whole file each time I save it - causing unnecessary overhead if I have to rewrite the usually static Members and Books.
Even with my new object model my original problem is not solved. If I am saving the Loans to a seperate file I will have to use the unique identifiers of the Books and Members to reference them. When I want to load the Loan objects again what would be the best way to go about this? Should I load the loan details and then loop through the Members and Books (which would be loaded first), until I find the correct object to reference for the Loan, and THEN create a real Loan object?
Thanks for your suggestions
Daniel
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Sure,
1) It is a school project, but also a bit of a hobby project. (the requirements for our school project are very low so I'm trying to do something that challenges myself!)
2) I'd like to be able to scale to at least a thousand books and a few hundred members (I realize that pretty much rules out any sort of serialization as it's very slow). I know ideally I would use some soft of database, but part of the requirements for the project is that I use plain old files.
3) Definitely a single-user system, that can only be accessed by one person at a time.
Thanks
Daniel
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Maybe a single XML file would be better suited to your needs.
Something like:
<library>
<members>
<!-- Member List -->
<member id="1" name="tristan"/>
</members>
<books>
<!-- Book List -->
<book id="1" author="me" name="mybook"/>
</books>
<loans>
<loan book="1" member="1"/>
<!-- Loan List -->
</loans>
</library>
You can then load the entire document into an object model, XmlDocument object, query it with XPath or many of the other xml operations. It also keeps the relations intact.
Hope that gives you some ideas.
Tris
-------------------------------
Carrier Bags - 21st Century Tumbleweed.
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Hi
Maybe I need to dig up my old varsity handbooks "Coding 101" but posting is easier 
I want to inherit an class-A (cause I want to use it's methods in a class-B), but I don't want it's methods exposed past class-B. I.e. Dim o as ClassB, if I type "o." it should only list class-B methods. Is there a way to do this, maybe it is not called inheritance? (PS: Using VB.NET 2.0)
Francois
Happy Coding!
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instead of inehritance, you can use delegation (or aggregation), i.e. Class B will contain a reference to an instance of a class A object and delegate it to do the requested work. This way B will expos no A methods.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
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If I understand you correctly you're saying "Dim o as new class-A" and then use "o.methodA" in class-B. I did think of this - but was wondering if there was another ("cleaner") way to skin the cat? 
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This is clean. Object aggregation it's often a good design alternative to complex class hierachies.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
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You only use inheritance if B "is a" A. Not if B "has a" A.
Inheritance is also sometimes called generalization, because the is-a relationships represent a hierarchy between classes of objects.
Source[^]
led mike
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Then what about private inheritance in C++? This does exactly what the OP is after.
Steve
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I am not sure what you are getting at. 
led mike
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