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I have to write this essay type thing and part of it wants me to explain:
Now i get the difference between distributed/centralised, but whats the difference between centralised and client server? Google hasent been much help so far :(Quote:
The differences between centralised, client server and distributed database configuration
Cheers.
Centralized means the data is in one place. Client server just means the clients are in a different place than the data. The statement above is worded poorly, but perhaps they mean the difference between local database and client/server. (?)
Yeah, thats kind of the impression I got. That maybe a centralised database meant users had access on a LAN only; not the net. However they would still both be centralised so its a little confusing. Still, I think I may as well go with that idea.
A centralized database system is the traditional database schema in which the database at located in one place. It is not to say the database may not be distributed among several servers, mind you. It simply means the database is considered one unit managed by one DBMS in one location and to which clients connect.
A distributed database configuration is achieved when there are several database servers replicating (or not) information between themselves and each with its own DBMS to which clients connect. Many companies starting at a given size now operate in this model. Branches or small offices hold their own - usually - stripped down version of the main database and data is usually replicated through scheduling.
Mind you that it is irrelevant how these databases are connected. WAN, LAN, Internet, is all the same.
I have no idea what a client-server database configuration is. Only thing I can think of is the client being some sort of filter through which requests to and from the database are passed. In that sense, users would connect to the client and not directly to the DBMS.
I might guess that "client server" is in contrast to an embedded database, but then there was no mention of the latter in the question.Quote:
I have no idea what a client-server database configuration is. Only thing I can think of is the client being some sort of filter through which requests to and from the database are passed.
I'm going to have a go at defining the three terms:
Centralized database.
I guess the old-fashioned mainframe solution would classify as centralized database - that is, you have one large computer to which you connect a large(ish) number of terminals. Everyone is working directly on the machine that holds the database, and the data never really leaves the mainframe machine [it gets displayed on a terminal, which is directly connected to the mainframe].
Client/Server database.
Client/Server DB system relies [traditionally] on a single database-server, which passes information to a client machine, where some of the data processing is done [e.g. verifying data-input, formatting data to be displayed/printed]. This reduces the load on the database server machine, as it doesn't need to perform any processing other than giving out and receiving data.
Distributed database.
Takes the client/server concept one step further by keeping multiple databases, where each database serves a set of clients. Generally, keeping the different databases in sync is one of the challenges here. The benefit is that the database can be (more) "local" to the user.
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Mats
Thanks for the input guys.
Mind you, while true, other models also classify as centralized DBMSes. Namely:Quote:
Originally Posted by matsp
- Several replicated SQL Servers operating through load balancing hardware
- Several SQL Servers in a DBMS cluster
- The MySQL server in your machine
- These boards database
Except that most of those are used as Server/Client systems [most often the DB for a forum is not on the same machine as the Apache server, for example].Quote:
Originally Posted by Mario F.
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Mats
Yes, they are. But the term "client-server" doesn't apply to a DBMS to define its physical organization (as does centralized and distributed). It instead defines the DBMS access configuration. So the author of that question either means something completely new to me, or didn't formulate the question correctly.
So you don't think my three definitions are what the original poster's question refers to?Quote:
Originally Posted by Mario F.
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Mats
Yes. To start with.
I also think your definitions are wrong, with the exception of the distributed model.
I disagree with your first two definitions as well. Any model with a centralized data source can be a centralized database (even with remote clients). Also, nothing about the client server model dictates that data must be centralized.
Centralized v.s. distributed is one issue. Client/server is totally orthogonal which makes the meaning of the sentence in the initial post difficult to understand.
The question could probably have been formulated as "The differences between centralised and distributed database configuration, client/server and embed access models"
As it is, it looks a little like asking "the difference between big, small and red apples".
Could it be that the initial question is about the difference between "centralized, client-server" databases and "distributed" databases?
That too!
I still think the three categories may be what I described. I may not have used exactly the right words, but say 20-30 years ago, a database system was something you couldn't use a PC to access [other than as a PC terminal application accessing a minicomputer or mainframe].
This then progressed into client/server solutions, where a central database is partially processed locally on the client, whilst the data is stored in one central point.
The next extension to that is a distributed database, where data is held in various locations - either that some data is in one place and some data in another place, or that all the data is available in multiple places - just pick the nearest.
Yes, there are many ways you can make up the hardware/software solutions for a database. But I don't think that is what the question is about.
I interpreted the question as "how has databases processing changed over time".
Mike_G: Does any of this make any sense in relation to what you have been learning in class? If not, perhaps you need to get some clarification from your teacher.
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Mats
Nah, I have no idea. All we do in class is make up SQL queries. We havent done any history of databases or anything. Guess I should really go find out what they expect from me.Quote:
Does any of this make any sense in relation to what you have been learning in class? If not, perhaps you need to get some clarification from your teacher.
You all seem to make good points; its just a matter of how you interpret the sentence.
Yes, and as we all know, even the simplest sentences can be misunderstood sometimes. In this case, it's quite possible that all of the suggestions are wrong, or that one or another of the alternatives is right.
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Mats
Simple solution: email your professor and ask him how the question should be interpreted.