Ask Question. Asked 11 years, 8 months ago. Active 11 years, 8 months ago. Viewed 4k times. Improve this question. Marcos Roriz Junior Marcos Roriz Junior 3, 11 11 gold badges 49 49 silver badges 74 74 bronze badges. The wikipedia page is quite brief, and describes it well en. I wouldn't have to read tons to find it. Add a comment. Active Oldest Votes. Improve this answer.
Jim Ferrans Mark Mark 2 2 gold badges 9 9 silver badges 19 19 bronze badges. Radi Radi 6, 16 16 gold badges 58 58 silver badges 89 89 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. In order to understand why EJB is so attractive to developers, we need some historical background. We'll go over the two types of EJBs: session and entity objects. You'll also read about home and remote interfaces, which create EJB instances and provide access to the EJB's business methods, respectively.
By the end of the article, you'll have an idea of how extensible servers can be built using Enterprise JavaBeans. But first, a look back in time. In the beginning, there was the mainframe computer.
And it was good. Or as good as it got, anyway. The state of the art in information processing through the s consisted primarily of big, expensive machines used by large organizations to support their daily business operations.
Minicomputers and timesharing in the s increased the accessibility of computing power, but information and processing were still centralized on individual machines. The first personal computers in the s quickly cluttered the corporate landscape with thousands of tiny islands of information, all tirelessly churning out reports of variable quality, losing critical data when they crashed, and quickly becoming inconsistent with each other.
Client-server systems are now commonly composed of various numbers of tiers. The standard old mainframe or timesharing system, where the user interface runs on the same computer as the database and business applications, is known as single tier. Such systems are relatively easy to manage, and data consistency is simple because data is stored in only one place.
Unfortunately, single-tier systems have limited scalability and are prone to availability hazards if one computer's down, your whole business goes down , particularly if communication is involved.
Such systems are still common. One garden-variety type of two-tier server performs most of the business logic on the client, updating shared data by sending streams of SQL to the server.
In such a system, a properly designed client can be modified to reflect new business rules and conditions without modifying the server, as long as the server has access to the database schema tables, views, and so forth needed to perform the transactions.
The server in such a two-tier system is called a database server, as shown below. Database servers have some liabilities, though. Often the SQL for a particular business function for example, adding an item to an order is identical, with the exception of the data being updated or inserted, from call to call. A database server ends up parsing and reparsing nearly identical SQL for each business function. For example, all SQL statements for adding an item to an order are likely to be very similar, as are the SQL statements for finding a customer in the database.
The time this parsing takes would be better spent actually processing data. There are remedies to this problem, including SQL parse caches and stored procedures.
Another problem that arises is versioning the clients and the database at the same time: all machines must shut down for upgrades, and clients or servers that fall behind in their software version typically aren't usable until they're upgraded. An application server architecture see the next image is a popular alternative to a database server architecture because it solves some of the problems database servers have.
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