Often under the Delphi Network database application development or once used Borland Midas technology friend, to Asta should not unfamiliar.
If it is based on ado.net or O/R mapping to achieve the DAL is Shaolin, Wudang authentic method, that Asta has a point to teach the "big move" flavor: The entire DAL in the data access almost completely thrown to another place (and the return of a slight difference, But also calculate another kind of diversion J) to handle!
Most of the traditional DAL implementations are like this:
Asta the alternative, adding a "middle tier" in addition:
In general, the introduction of the middle tier is designed to increase flexibility and reduce coupling,
Asta is the use of this feature designed.
A key point of the above figure is the ASTA client and ASTA server
The "Network Connection", ASTA technology is the use of network characteristics, indirectly
Masks differences between different database systems, enabling developers to finish designing Dal
No need to know the existence of the database! This situation is a bit like a browser, completely not
With the knowledge that HTML pages are from IIS or Apache, you just need to know your
is to use the HTTP protocol to get HTML pages through the network!
In Asta, the browser is the Asta client,html page is the ASTA dataset (unlike the dataset in Ado.net, which can be considered as another database-independent representation of the data collection), and IIS, Apache is the ASTA provided by the different Asta server (currently supports most mainstream database systems, developers can also write their own Asta Server), the HTTP protocol is naturally ASTA client and ASTA Server communication protocol!
From the technical analysis, one of the purposes of the ASTA architecture is to use the protocols provided by them to mask the network communication protocols of different database systems, so that the client (DAL) can completely get rid of the communication problem when writing the application of the network database.
(the author remembers,. NET, each time you write an Internet-facing SQL Server application, in addition to configuring the connection string, you install the SQL Server Client Network Utility specifically on the client to configure your Internet connection, not to mention SQL Server exposed port security problems, that's what it's like to do. J.
Writing programs under Asta is very comfortable, as long as you know ASTA server address and port, and then provide a certain permissions of the user name, password (ASTA with the certification system, developers can also write their own authentication/authorization module, Even directly using the validation mechanism provided by the database system), you can immediately get any data information of any database! Furthermore, once the database system changes (such as switching from SQL Server to Oracle but not including changes to the database structure), the client does not need any modification at all!
ASTA technical deficiencies are also evident: as a result of the introduction in some cases
(such as a large time to return data) is enough to kill the "network middle layer", so that open
When developing large applications (especially for Internet-facing enterprise-level applications)
Need to be especially careful, after all, comfortable at some time is to pay a certain price!
Interested friends might as well go to this website to see:
Http://www.astatech.com
Ø.net remoting/webservices
Originally not prepared to take out the. NET remoting/webservies to join in the fun, after all, these two technologies are not for the DAL tailor-made.
Helpless, it is just to see a friend so used, and then think, found that there are some reasons, take out with everyone to participate in detailed.
In fact, although Microsoft hype XML webservices, but in terms of technology, in fact, as long as the discussion of the. NET Remoting one can, XML webservices nothing more than in the. NET Remoting using the HTTP + A special case of soap communication protocols.
The. NET remoting can be applied to the DAL for two purposes:
(1) Want to achieve cross-platform data access, because the dataset in the Ado.net can be serialized, through remoting or webservices can restore the scene on the client;
(2) Reduce server pressure and increase system flexibility.
It's kind of like the ASTA technique above, but the protocol here
Replaced by. NET Remoting protocal. But even in this way,
There is a difference between ASTA flexibility and, after all, remoting to
To register the Access interface for each DAL at the client, once the interface
Changes, the interface must be registered again!
Therefore, the author's advice is: try to avoid using. NET Remoting to
Build the application's Dal module (if it is business Logic Layer, do not
Existence of this problem) unless it is really "forced" (e.g.: Must be in the DAL
Layer to implement distributed computing or customers insist on using. NET Remoting J)!
The following sections are being written because of time constraints!
L My plan (not finished, writing ...) ）
U Synthesis of existing technologies
Ø Add a new DAF Layer:data Access façade above the DAL
n Use Dataset/datatable/dataview + Cache Management
n Use Objectspaces/eco + ado.net + Stored Procedure
O......
U Use ready-made frame
Ø Open Source project recommended use OPF (foreign)
Ø recommended use of commercial products Grove (domestic)
O......
U design your own persistence layer
Ø If you want to design your own wheels, then the best reference is this article: Http://www.ambysoft.com/persistenceLayer.pdf
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