Organization of the interaction between managerial system data

Problem independent access to data and technology ODBC

The Process of the development and developments any DBMS inevitably brings about need to solve a problem interactions with data, created and operated within the framework of other programme systems, or, as else speak, to problem of the access to external source data. This, in turn, defines the principle requirement, which must satisfy applied DBMS. The Programme procedures information handling, created within the framework of DBMS, must be greatly independent from format prestored data.

Execution of this principle allows:

• about first, with least expenses to realize transition from one DBMS to another, need for than, possible, appears when scaling earlier created software for enterprise and companies of qualitative other size
• in second, successfully solve problems to integrations two and more independent programme systems

The most Most important instrument independent access to given technology ODBC became from programs (Open Data Base Connectivity), created by company Microsoft. Her(its) principle scheme изображена on fig. What follows from it, within the framework of ODBC:

• programme exhibit directly interacts with traffic manager driver, sending him ODBC-call
• traffic manager driver to have charge of dynamic loading necessary ODBC-driver, through which addresses to DBMS (server database)
• ODBC-driver executes all call ODBC-function, "translates" them on language of the source data
• DBMS keeps and removes given in response to requests on the part of ODBC-driver (or returns code of the error)

At present in composition suppressing majority managerial system data enter corresponding to ODBC-drivers.

Thereby, when work with the base given through ODBC-driver she emerges as a certain virtual source data, which possible control by means of SQL like commands.

The Task ODBC-source given (DSN - data source name) is an action, which is realized facility of the operating system, controlling computer. In particular, in operating ambience Windows 95/Windows 98 for this in Panels of management is provided point Sources Given ODBC (32 разр), from which is caused Manager of the sources given ODBC. With his(its) help can be given:

• user DSN - a source data, available only current user on current computer
• file DSN - a source data, which can use together different users, beside which are installed alike ODBC-drivers
• system DSN - a source data, available all user and service of the current computer

Access from MS Access to source given in format other programme exhibits

Two principle possibilities of the work are provided In MS Access with external data. This import data and relationship with external table data. Both modes available from menu main window database: File > External data.

In the event of import occurs making the copy external given in newly created to table. Amongst advantage of such decision can be named:

• accessibility of whole arsenal of the facilities DBMS Access at manipulate imported data
• high speed when referencing to him
• independence from source source data

However, gaining specified advantage, we simultaneously get and potential problems, connected with maintenance of urgency and correspondences to to each other two parallel mineses one and same information. Much often like problems turn out to be unsolved.

Eсли urgency data is for us critical factor, that necessary to use other way of the work with external given - a relationship. In this case in database is added only reference to external sources data and work with they come of help special driver. The drivers enter In supply MS Access traditionally for work with data, created in format Paradox" Excel, dBase, FoxPRO, as well as in text (*.txt) and гипертекстовом (*.htm) format. The Database Paradox, Excel, dBase, FoxPRO and some other format also name the database with subscripted-consequent organization (engl. - ISAM - Indexed Sequential Access Method). Specific IS AM-drivers, taking into account concrete particularities enumerated format to organizations data, as a rule, provide high efficiency and speed when work with them. Simultaneously the possibility of the work exists in Access with extensive ensemble of the universal sources data, for which are installed ODBC-drivers. For this at instruction of the type of the file, with which is fixed the relationship, necessary to choose the Database ODBC.

"Charge" for using of technologies of the collecting with external data are a restrictions of the possibilities on structure management added tables, as well as dependency from condition of the most external source, to which we are connected.

Technological decisions on organizations of the access to data

We shall Consider a little in detail architecture of the access to given in Access. Shematichno she is submitted for fig. In presented scheme block user interface personifies the visible part DBMS that is to say that, with than user interacts directly (the forms, reports and the other objects). Under хранилищем given are understood file (the files), containing tables given (for instance, in Access this mdb-files).

The Vault - certain passive element, in him given simply contains. Realize the manipulates with them - a problem of the processor database (or, as else speak, kernel database). He транслирует the commands of application in physical operations, directly changing file (the files) vault data. The Main dignity of the described scheme is independence of application from type database, to which she addresses: will this given in internal format Access or given some other structures - in application are used one and same objects and access methods to him.
В MS Access используется процессор, получивший название Jet (Join* Engine Technology). Он реализован в виде набора файлов динамически компонуемых библиотек (DLL), которые связываются с прикладной программой Access в период ее выполнения. В состав процессора Jet входят процессор запросов SQL и процессор обработки результатов, возвращаемых этими запросами.

Considered earlier model of the object interface of the access to given OAO presents itself programme superstructure on processor Jet. Jet also realizes described in 7.3.1 possibility on access to external given in format ISAM and source given ODBC.

The processor Jet versions was used For functioning(working) DBMS MS Access 97 3.5 for 32-class exhibits. Amongst principle advantage of the new version can be named:

• ODBCDirect - an alternative mode DAO, which gives the possibility of the direct address to the source given ODBC in pass-by kernel Jet. This allows in some cases to optimize process of the work with given to account of the use the specific features removed ODBC-sources
• for database, operated by processor Jet, are determined new objects, characteristic and methods, allowing use new possibilities partial репликаций

Also follows to note that in Jet marketed technology Rushmore - a special methods of management request, which allows much effectively select the Sets of the record when use in their критериях of the certain types of the expressions.

The author: Y.N.Antonov Is added: 21.06.2008