Discussion on data access interface system and data object Model--[2]

Object | access | data | system
Research on data access interface system and data object Model (Beat 1.0)


81_RedStar81@163.com
TomHornson.student@www.sina.com.cn


Personal Anthology:
http://www.csdn.net/develop/author/netauthor/RedStar81/









A discussion of data access interface System



1.Open Client/open Server



c/S structure of the middleware is specifically configured on the client and server side of the package (Note 2::). Sybase Open Client/open Server makes interoperability possible in distributed heterogeneous environments. Here we briefly describe the working principle of Sybase C/s middleware. Open client is the client API that enables client applications and Third-party tool software to send SQL statements and Remote Procedure calls (RPC) over the network to Sybase SQL Server or through an open Server application (to take advantage of the Open Server development for application of flags to other data sources (database systems or objects managents or normal data stores) or other types of servers. There are two very important behaviors that occur from the open Client API call to the channel transport, TDS ( The same as Telnet, FTP, etc. belong to the Application layer protocol, the formatter is responsible for converting the upper layer of SQL or RPC, which is marked by API call, into TDS message packets and supporting a variety of transmission protocols, the TDS package is formatted according to the package of the corresponding client and server-side communication protocol. Naturally on the client, Before the channel transmission behavior occurs, there are many behaviors with other network applications (see details of the Protocol model). Open server is a server-side API that allows a client to send a request to a non-SQL Server data source or other type of server in SQL statement or RPC form. The data source or special server is then sent back to the client for status and data in standard TDS format. Open Server can constitute an ideal C/s structure environment, that is, all clients can interact with all servers in a unified manner, and all servers can accept client requests in a uniform manner and return results to the client in a standard format. As an extension, we'll introduce a little bit about open Client/open server knowledge so that readers can see some historical technical factors in the ODBC system analysis discussed in detail below. In fact, as mentioned above, Open Client/open server is an API, until Sybase system 11, The mature API contains the client's db-library, client-library, and server-side server-library as well as the public cs-library. The important feature comparisons are listed below

1.client-library is superior to older db-library and client-library is not SQL-independent.

2.db-library does not support server-side cursors. Client-library fully functional, supports all types of cursors, including sensitive and insensitive cursors

3.Open servers are server-side APIs that are used to develop server-side applications. Provides consistent data access framework capabilities. The Open Server application can both communicate with Sybase and non-Sybase communications and Sybase SQL Server Connecting to other data sources requires the development of the Sybase open Getway using the Open Server API.

Here a little mention, through the implementation of the Open Client/open server functions, the database system service characteristics, ODBC, such as the late appearance of interface system, the current database system service characteristics of the comprehensive analysis and comparison, you will send

Open client application (open client application, contains Sybase open Getway, Normal DataSource application, Mail Open client, and some of its unified data The application of the access framework in the later data interface system can also achieve the same function but the implementation of the way, the function of the implementation of the body and its distribution is very different. Even now there are some shadows.





2.ODBC (Open DB Connectivity: Open database connection)



ODBC is an important part of the Microsoft Windows Open Standards Architecture (wosa,windows Open service System), which was released by Microsoft Company at the end of 1991, In a few short years it has become the de facto industrial standard. It establishes a set of specifications that provides a standard API (supported SQL) for tiering (with increased data service capabilities), which addresses the nonstandard core of embedded SQL interfaces that data application systems use to access any ODBC driver provided ( A set of DLLs. In the past, it was necessary to master the corresponding data access APIs for the development of different database systems. In fact, the ODBC system can be viewed as a unified data access interface, and making this unified data access possible is the database products vendors to provide the corresponding ODBC Provider (ODBC Provider is ODBC-driven), but ODBC is generally available only for relational databases, and it is difficult to access object databases or other non relational databases or data systems. The following is a brief description of the composition and working principle of the ODBC system. ODBC specification illustrates that the ODBC system has four components: application, Driver Manager, Driver, and Data Source. (pictured below).



The high-level development workflow combined with reality is as follows:

1. The data application system first obtains the DSN established in the ODBC Data Source Manager (the details of the connection to the data provider contain the database location, database type, and the corresponding ODBC driver, and so on), and then Driver Manager relies on a communication called Database independence ( The technology of the database indepedent Communications Technology) is associated with the data source (which involves problems with multiple agent objects on both the client and server side, as described in the following figure).





2.Driver Mangaer invokes a specific ODBC driver to convert the ODBC standard API into a function call that applies to a specific database system (where the database features are also translated, such as SQL syntax differences), and then sent to the data source via the client's request agent.

3. Data source database Agent processing operations, the results returned to the client request Agent, and then up to Driver (there will be translation and standardized error code behavior), Driver Mangaer returned to application.

What needs to be explained is that the behavior of defining and manipulating cursors, maintaining transactions, and being responsible for any interaction with the necessary software layer that accesses the data source (including software that interfaces with the underlying network or file system) is also done by the driver.



Describe workflow in conjunction with ODBC API call Order: initialization (allocation environment---> Assigning connection handle---> Connection to Server---> Assignment statement handle)-------->sql processing (statement processing and retrieval)--------> termination (Releases the statement handle---> Disconnects the server---> releases the connection handle---> Release environment).





3.OLE DB (Object Link and Embedding DataBase)



With the development of network technology and database technology, the application system is becoming more and more demanding in data integration. It is necessary to place different formats (such as files, spreadsheets, e-mails, and emails in relational databases and operating systems). Data integration of multimedia data and directory service information or IMS and VSAM data in host systems, etc. the traditional solution is to use a large database system to move all this data to the database system and then access the data according to the Operation database. While this can be done in a uniform manner on the data, this indirect access has brought many problems, such as the data update is not timely, spatial resource redundancy and access efficiency is low, etc.

At this time, Microsoft's Universal Data Access Technology (UDA) came into being, enabling data applications to access a wide variety of data through data providers that implement the standard OLE DB interface, regardless of where the data resides, or whether data transfer or replication or transformation is required.

OLE DB, as a data access interface system, embodies the philosophy of Microsoft's Universal Data Access (UDA) strategy. UDA is able to access various types of data through a standard interface. With the ODBC system it also provides a set of standard APIs, but the OLE DB API is completely COM based, It is characterized by the use of multi-layer models. On one side of the COM communication layer is the data consumer. This COM based communication can be summarized as an operation performed on abstract objects such as DataSource, Session, Command, and Rowset. This occurs when the user connects to DataSource, opens the session, issues a command, and returns the data rowset.



In fact, OLE DB is a system-level programming interface that defines a set of COM interfaces that encapsulate a variety of data

system access, which sets standards for data consumers and data providers, and OLE DB provides a set of standard

Service components to provide queries, caching, data updates, transactions, and so on, so the data provider only needs to implement a

Some simple data manipulation. All data control capabilities are available on the user side.





Cond:







4. JDBC (Java database Connectivity:java DB connection)

Ii. discussion on data object model (to be continued)
Appendix: US Famous Database product Chronicle (Reference)