Tài liệu Oracle Unleashed- P17 pdf

The objects of Oracle Objects for OLE have their basis in the Data Access Objects (DAO) of the Microsoft JET SQL engine. JET parses queries and contains its own SQL syntax. JET performs query joins locally; using ODBC, JET might not be able to make full use of features available in a particular database. JET implements a number of objects used to represent and manipulate the objects of a database. The DAO concepts are good, but their implementation is poor and they suffer from having to represent data in the form of flat files up to relational database. Oracle Objects implements some, but not all, of the DAO but does so from a client/server point of view and does so realizing the potential size and organization of Oracle7. Oracle Objects for OLE does not contain its own SQL engine and relies on Oracle7 to parse all queries using its syntax. If an application only needs to communicate with Oracle7, why introduce an intermediate SQL engine with its own syntax? Oracle Objects for OLE does not perform local query joins and can access practically all SQL and PL/SQL (Oracle Procedural Language SQL) features. Because Oracle7 can potentially contain millions of rows and because a server is generally more powerful than a client, how could you and why would you perform joins locally? Finally, why not make use of Oracle-specific features and functionality such as PL/SQL? A larger comparison of the Oracle objects and DAO is done in the following chapter, but a brief summary is appropriate here. Discussion of three objects shows the most overlap. These objects are the database, the dynaset, and the field. Within DAO, a database object is used to represent an open database file and a connection to a database, as well as to control database-wide permissions and functionality. A dynaset object is used to represent the return set from a SQL select statement. (A snapshot object also exists, which is basically a read-only dynaset.) A field object is used to represent a single column of a query that has been returned as a dynaset. Using Oracle Objects for OLE, an OraDatabase object is used to represent Oracle7 and to provide options on row locking and column defaulting. An OraDynaset object is used to represent the return set from a SQL select statement and to implement backward scrolling cursors, which Oracle7 does not natively support. (Instead of implementing a snapshot object, you can mark the dynaset as read-only.) An OraField is used to represent a single column of a query that has been returned as a dynaset. In addition to those objects, DAO has a tabledef object that represents the definition of a table—columns and their data types. Oracle Objects for OLE does not have any such object, although it would be an interesting addition. Adding this type of object would not necessarily violate Oracle Objects client/server model because you still could store the actual table definition in Oracle7, and use the local object to manipulate it. DAO also contains a querydef object, used to save a query for easy reuse. Oracle Objects does not contain such an object, but Oracle7 does have views that are an excellent equivalent. This way, code is stored on the server and can be used by an even wider range of users and does not need to be stored with the application. Again, Oracle Objects relies on Oracle7 to provide functionality where appropriate. Data Access Using OLE Although the acronym OLE (Object Linking and Embedding) does not mention it, OLE Automation may be the most important feature of that technology. OLE Automation enables the implementation of an interface that is registered with the Windows system and is instantly available to any application capable of being an OLE (Automation) client. This means that the objects, methods, and properties of OO4O are presented consistently across applications such as Microsoft Visual Basic 3.0, Access 2.0, and Excel 5.0. Code written using OO4O for accessing Oracle7 can be run unchanged in any of those and other environments. Why OO4O Uses OLE (and Not Other Methods) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. OO4O provides an interface that can be used unchanged in multiple environments, as just described. The amount of code you can reuse is large and the learning curve small. Dynamic Link Libraries (DLL) also provide extensibility, but they do not have a specification for registering and querying their interface. Having no standards has led many applications to implement DLL interfaces differently so that even if the DLL can be used, code is not very portable. OLE 2.0 is still a developing technology with Microsoft adding feature support (distributed objects) and more vendors adding application support. Eventually, OLE will become the basis of Microsoft's next-generation operating systems. How to Use OLE Automation Using OLE Automation in the products that currently support Oracle Objects is quite easy. OLE objects are declared just like integers or strings and can be manipulated using whatever methods or properties are available with a dot notation. The following code shows how to create an OraDynaset and loop through records: Dim OraSession as Object Dim OraDatabase as Object Dim OraDynaset as Object Set OraSession = CreateObject("OracleInProcServer.XOraSession") Set OraDatabase = OraSession.OpenDatabase(ÒOracle7Ó,"scott/tiger", 0&) Set OraDynaset = OraDatabase.CreateDynaset("select name, address from addrbook",0&) While Not (OraDynaset.EOF) MsgBox "Name = " & OraDynaset.Fields("Address").value & " Address = " & OraDynaset.Fields("name").value OraDynaset.MoveNext Wend The dot is used to append a property or method name to an object. If the next-level method or property returns another object or collection of objects (like OraDynaset.Fields), then further clarification may be needed to identify a particular object (in the case of a collection) or the desired property of the object (the value). Performance Overview Common questions are "How fast is it?" and "How does it compare to X?" and "Why is it slower than Z?". This section provides no easy answers, just recommendations to help you make the correct decision based on the correct information. Making an Accurate Comparison Although Oracle Objects for OLE is based on DAO, its implementation is significantly different. For example, an OraDynaset has a local data cache that stores all fetched rows locally to implement backward scrollable cursors. A DAO dynaset only stores a window for data locally and refetches based on a primary key when rows are needed. An OraDynaset provides read consistency and a DAO dynaset does not. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. You can create an OraDynaset with three calls. Internally, using OCI, the implementation requires much more code. Many database access methods and products are available, and none is implemented exactly the same as Oracle Objects for OLE. A fair comparison, and one that is done often, is to DAO/JET in non-SQLPASSTHROUGH mode. These two methods are related most closely in terms of functionality; just make sure you understand the implementations of both methods before making comparisons. Considering Oracle Tips Although database tuning and SQL optimizations are beyond the scope of this documentation, you should remember a few basic tips when performance is an issue: ● Don't select any more rows or columns than necessary. Oracle Objects for OLE fetches rows as needed and caches all rows locally. ● Moving the processing from a flat file or single-user system to a remote multiuser database causes the network involved to play a major part in performance. ● Oracle has documentation on query optimizing or database optimizing. If performance is very important, maybe your table needs an index or maybe the database parameters need tuning. Whatever the situation, remember that Oracle Objects for OLE is mostly a piece of middleware that uses the server for processing. The performance of all components (hardware locally, network, database, hardware remotely) is important. Development Issues Oracle Objects for OLE development requirements are minimal when compared to those of the additional software required. OO4O has all the typical development requirements (environment, disk, memory) plus it needs a host application to drive it. If your current hardware/software already supports connecting to Oracle7 and can run an appropriate host application for Oracle Objects, then you should have no problem adding Oracle Objects to the equation. You can find Oracle Objects for OLE typically packaged by itself or bundled with various versions of Personal Oracle7 and the Oracle Workgroup Server. Because you may not have Oracle7 or you may want to run it on your own system, these bundles are excellent values. Don't assume Oracle Objects is included in all similar and future bundles of these products, because the bundling changes at Oracle's discretion. Oracle Objects for OLE also is available as a 90-day trial product on Oracle's World Wide Web site at www.oracle.com. Again, this offering is subject to change by Oracle. Software Requirements Oracle Objects for OLE is not a complete development environment but a development aid. OO4O requires a host application or development environment with which to build one, plus access to Oracle7. Oracle Objects basically requires a system capable of running 16-bit Windows applications that can also connect to Oracle7. These systems include but are not limited to Windows 3.1, Windows for Workgroups, and Windows NT 3.x. Host Environments The Oracle Data Control can theoretically work in any environment that supports level III custom controls, but it is documented to work only within Visual Basic 3.0. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Microsoft Visual C++ 1.5x supports level I custom controls only and cannot load other higher-level controls. The Oracle In Process Server requires any application that can support scripting to an OLE Automation Server. These programs are Visual Basic 3.0 (Standard or Professional), Access 2.0, and Excel 5.0. Word 6.0 can act as an OLE Server, but it does not support scripting to an OLE Server. You could use C or C++ to write your own OLE scripting client, but you probably should not because no help is offered in the product documentation. If you want to try, C++ is easier because of the automatic code-generation tools shipped with most popular development environments. Even easier than writing an OLE client yourself is to use the Oracle Objects C++ Class Library. The class library provides the same objects that the OLE Server does and takes care of various OLE initialization tasks and some memory management. The C++ class library also contains a class that enables dynaset-to-data widget binding much like the Oracle Data Control. The Oracle C++ Class Library contains two components and is built in two flavors. The first component contains classes that are implemented as a DLL over the objects found in the OLE Server. The second component contains classes to enable the dynaset-to-data widget binding. The dynaset-to-data widget binding functionality is implemented as a static library and implementations are provided for MFC (Microsoft Foundation Classes) and OWL (Object Windows Library). Each of the components has been built for use with Microsoft Visual C++ 1.5x and Borland C++ 4.x. These two formats are necessary because of differences in C++ name-mangling that affects how classes are exported from a DLL. The documentation says that no other compiler is supported, although others may work if they follow the calling conventions and C++ name-mangling conventions of MSVC++ or BC++. The first production release of OO4O (1.0.42) did not work properly with Borland C++ 4.5 (you received the error Undefined symbol: v_U_U_W_Dispatch when linking). This problem was fixed in a later patch (1.0.55). Remote Database Access If your database is a remote server, Oracle SQL*Net for 16-bit Windows is required. Some of the original packaging may have suggested that Oracle SQL*Net was built into the product, but this is not the case. Oracle Objects for OLE does not depend on any particular protocol, version (V1 versus V2), or patch level of Oracle SQL*Net. You can use any valid combination of SQL*Net client to SQL*Net server that is available. Local Database Access If your database is local, you probably don't need any additional software to connect to the database. For example, although Personal Oracle7 for Windows 3.1 is Win32s-based, it contains a layer to communicate locally from 16-bit applications to the 32-bit database. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. The exception is if you are developing on the same machine as the server. For example, if you are developing on Windows NT, you are still accessing Oracle7 in a client/server mode and you still need Oracle SQL*Net as just mentioned. Memory Requirements OO4O is actually a very small piece of software. In terms of size, the Oracle Data Control is only about 64K, the Oracle In Process Server is about 239K, and the C++ Class Libraries for Borland and Microsoft are 74K and 137K respectively. Does this mean that the memory requirement for OO4O is no more than 300K? No, unfortunately it doesn't. Although OO4O is not a large amount of code, it does store data in memory per the settings of its cache parameters in ORAOLE.INI (discussed in more detail in Chapter 47, "OLE Server"). You can tune these settings so that data is swapped to disk, but performance suffers. An exact number is not possible, because operating and bookkeeping overhead is involved. After reading the "Tuning and Customization" topic in the product documentation, my best estimate is MemoryUsage = (SliceSize * PerBlock * CacheBlocks). Because OO4O depends on other software to operate, you must take into account the memory requirements of the other software. Check the documentation of the host application you're using to determine its development memory requirements. Disk Requirements The complete OO4O package has typically been distributed on four high-density (1.4M) disks. Although almost all the files on the disks are compressed, a closer look reveals that most of the files are not part of OO4O proper, but either Microsoft OLE 2.0 or the Oracle Required Support Files (RSF). A complete OO4O installation including all sample applications, Oracle Required Support Files, and Microsoft OLE 2.0 requires about 8M of disk space. You may not use that much disk space for several reasons: OLE 2.0 is most likely included with your host application or development environment; the Oracle Required Support Files are shipped with almost every Oracle Windows application (which you may have); or you may choose not to install all the sample applications (which are about 1.5M by themselves). Considering that a typical installation of Microsoft Visual C++ 1.5 needs 45M of disk space and a Visual Basic 3.0 needs about 12M, OO4O does not require an unreasonable amount of space. Finally, Oracle Objects for OLE swaps OraDynaset data to disk as it is fetched and cannot fit into memory. A reasonable estimate of disk space required for an OraDynaset is the size of the columns and rows of the data fetched. (This size is not necessarily the size of the entire OraDynaset if you have not reached the end.) The size of the data fetched is close to the size of the data from the first row to the farthest row reached. You don't necessarily need to add LONG and LONG RAW data, because that data is fetched only on demand. Because estimates are not easy to calculate, the best way to determine run-time disk usage is to try Oracle Objects in a simulated user environment. Deployment Issues Even though you have been developing with Oracle Objects and everything works fine, you need to make some extra considerations for deployment. Software Requirements The run-time requirements for Oracle Objects are very similar to the development requirements, except for the licensing or acquiring the needed components for connecting to Oracle7 on each client. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. The product documentation lists exactly what Oracle Objects for OLE files are needed and what Microsoft OLE 2.0 files are needed under the on-line documentation topic "Redistributable Files." Oracle Software Although run-time distribution of specific OO4O files is free, deployment of other required Oracle software is not. OO4O requires the Oracle7 Required Support Files for 16-bit Windows. You usually can obtain this software from the Personal Oracle7 package if the end user will be connecting to a personal database. Or you can obtain the software from the Oracle SQL*Net for Windows package if the end user will be connecting to a remote database. The Oracle7 Required Support Files are numbered for the various Oracle7 releases such as 7.0, 7.1, and 7.2. Because filenames typically change between releases, you must make sure that the RSF on the deployment system matches the one required by OO4O. OO4O originally required a version 7.1 RSF (up to release 1.0.57) and in the future could require a higher version. You can find out which version of the RSF your deployment system has by checking the release media or running the Oracle Installer (which stores a list of installed products and their versions). Host Environments Again, the host environments that are supported for development are the same for deployment. Some of the supported environments do have run-time versions; some do not. Of the known supported host environments, Visual Basic 3.0 (Standard or Professional) and Access 2.0 have run-time versions. Excel 5.0 does not. Microsoft Visual C++ 1.5 and Borland C++ 4.x can obviously build an executable that you ship. Always consult the particular host product documentation as to which files are needed and which are distributable because this information can change between versions. Visual Basic 3.0 does not ship with a complete set of OLE 2.0 run-time files. The file TYPELIB.DLL is missing. This point is mentioned briefly in the "Troubleshooting" topic of the on-line documentation and is well worth mentioning here. Check the on-line documentation topic "Redistributable Files" for complete details. Remote Database Access If your deployment system will be accessing Oracle7 remotely, then a copy (license) of Oracle SQL*Net is necessary. Even though this product may have been included with the bundle you purchased for development, Oracle SQL*Net has historically not been licensed for free distribution. The same requirements listed earlier in "Remote Database Access" for development also apply here. Local Database Access If your deployment system will be accessing Oracle7 locally, then a copy of that database (typically a Personal Oracle7 bundle) is necessary. Even though this database may have been included with the bundle you purchased for Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. development, the Oracle database has historically not been licensed for free distribution. The same requirements and exceptions listed earlier in "Local Database Access" for development also apply here. Memory Requirements As noted earlier in "Memory Requirements" for development, OO4O by itself has a very small code base and is highly dependent on the cache settings in ORAOLE.INI and the amount of data fetched. All other requirements listed in that section are valid at run-time because the OO4O code is the same for both. Disk Requirements As with almost every other deployment issue, disk requirements are mostly dependent on the host application and on the other required files. The complete set of run-time files for Oracle Objects is roughly about 400K, but the other needed files can run into multi-megabytes. Again, check the documentation of the host application and other software required because this information may change between releases. Summary Oracle Objects for OLE provides excellent access to Oracle7 from many popular applications. The interface is designed to resemble the Microsoft Data Access Objects, but it should not be judged strictly on its duplication of the DAO interface. Oracle Objects for OLE provides better integration with Oracle7, leverages more of the power of Oracle7, and uses one of the newest and most popular Windows technologies (OLE 2.0) to do so. A natural progression of this product would be to add more of the DAO interface and provide easier access to Oracle7 features. Oracle has made improvements even in the small patch releases and will presumably continue developing Oracle Objects for OLE for use on 32-bit platforms using OLE controls. This product is small but provides formidable competition to similar interfaces. Previous Page TOC Next Page Home Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Previous Page TOC Next Page Home ● 47 ❍ Oracle OLE Automation Server ■ Background ■ What Is an OLE Automation Server? ■ What Is an OLE Automation Object? ■ What Is an OLE Automation Collection? ■ Object Hierarchy ■ Types of Oracle Objects ■ OraClient ■ OraSession ■ OraConnection ■ OraDatabase ■ OraParameter ■ OraDynaset ■ OraField ■ Collections ■ OraSessions ■ OraConnections ■ OraParameters ■ OraFields ■ Dynaset Data Issues ■ Using Valid SQL Select Statements ■ Selecting Data ■ Editing Rows ■ Adding Rows ■ Deleting Data ■ SQL Parameters ■ Binary (LONG/LONG RAW) Columns ■ Transactions ■ ExecuteSQL() Method ■ Data Definition Language (DDL) ■ Data Manipulation Language (DML) ■ Stored Procedures/Functions ■ Some More Properties ■ Portability of Source Code ■ Host Environments ■ Performance ■ Database Performance ■ OLE Server Performance ■ OLE Performance ■ Error Handling ■ Application Errors ■ Oracle Errors ■ Comparison with DAO/JET ■ Differences Between Oracle Objects and DAO ■ Oracle-Specific Features Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. ■ Data Updatability ■ Data Access ■ Implementation of the OLE Server ■ Performance of the OLE Server ■ JET/DAO Migration Issues ■ Summary 47 Oracle OLE Automation Server The Oracle OLE Automation Server implements a number of objects used to represent the Oracle7 database and objects within it. The objects are high level and do not require the user to understand SQL processing steps such as parse, bind, define, execute, and fetch. The user must be able to provide database connection information and a SQL statement, then he or she can edit data using familiar methods such as Add(), Edit(), and Delete(). Background The objects of the Oracle OLE Automation Server are based on the Data Access Objects (DAO) of the Microsoft JET SQL engine. The concepts of DAO are good, but the implementation does not provide very smooth integration with Oracle and Oracle-specific features. The Oracle OLE Automation Server and its objects were designed for an Oracle database and provide tighter integration than DAO. What Is an OLE Automation Server? An OLE Automation Server is an OLE object (application) with exposed methods and properties you use to manipulate the object. After the methods and properties become available, you can manipulate the objects within the OLE Server from any OLE Automation client. What Is an OLE Automation Object? An OLE Automation object is an instance of a class of your application for which you have exposed methods and properties, which you use to manipulate the object. A useful feature of OLE Automation objects is a reference count. A reference count is kept so an OLE Automation Server can destroy an object when it is no longer used. For this reason, the Oracle OLE Automation Server has no Close () methods. When an object goes out of scope and is no longer used, the OLE Automation Server automatically destroys it. What Is an OLE Automation Collection? You use a collection object to manage other objects. A collection object can contain zero or more objects. By specification, a collection should support iterating through its objects and a count property to determine the number of objects in it. A collection also should support some form of indexing so you can access individual objects in the collection. You can index the various collections in the Oracle OLE Automation Server by name or number (0 to Count - 1). Object Hierarchy Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. The relationship between all the Oracle objects is hierarchical and rather straightforward, as shown in figure 47.1. Figure 47.1. Object Hierarchy of OLE objects. Only one OraClient object exists for all applications in the system. OraClient is created implicitly when the first OraSession is created. The OraClient object exists only as a root for all the other objects. One default OraSession exists per OraClient, but you can create other named OraSession objects. Database transactions are normally affected at the OraSession level. An OraConnection represents an actual connection to Oracle and may be shared by multiple OraDatabase objects. An OraConnection cannot be explicitly created, only implicitly, by creating an OraDatabase object. Database transactions can be committed at the OraConnection level, but it is not recommended. An OraDatabase object is created using a username, password, and database name. The OraDatabase object is used to control the connection (which can be shared among OraDatabase objects), to create dynasets, and to execute any other SQL statements. An OraDynaset represents the return set from a SQL select statement and contains one or more OraField objects. An OraField object represents one column of the return set of a SQL select statement. An OraParameter represents a SQL or PL/SQL bind variable and is valid for all dynasets under its parent OraDatabase. Types of Oracle Objects The product documentation is well-written as a reference guide, but it lacks discussion of the relationship that the following objects have with each other and with Oracle7. OraClient The OraClient object is more important to the OLE Server than to the developer. This object is the root of all objects on a given client system and is created implicitly by the OLE Server when the first OraSession in any Oracle Objects for OLE (OO4O) application is created. The OraClient object is accessible only from an OraSession object. The OraClient contains a collection of all the OraSessions of a particular application, but it does not enable one application to use for accessing the objects of another. The OraClient has only one method, CreateSession(), which has been duplicated as CreateNamedSession() and added as a helper method to the OraSession object. OraSession The OraSession object has much more importance to the developer than the OraClient. This object is the one that the developer most likely sees as the root of all objects in an application. An OraSession must be created first, and the initial one is the only object created directly by an OLE interface; the rest are created by methods of other objects. An OraSession is created with a call to CreateObject(), as this example shows: Dim OraSession as Object Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. [...]... s Summary Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark 49 Oracle Objects for OLE C++ Class Library In the last several chapters, you have seen what Oracle Objects is and how to use it from Visual Basic The same power is available to C++ developers through the Oracle Objects for OLE C++ class library Because this class library is based on the Oracle Objects for OLE product,... sub Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Comparison with DAO/JET Although the Oracle objects are conceptually close to the Microsoft Data Access Objects (implemented using the JET SQL engine), the Oracle implementation has a number of fundamental differences These differences affect, among other things, data access, data updatability, and Oracle feature access... environments, communicated directly with Oracle, and could access Oraclespecific features Oracle- Specific Features The JET SQL engine understands its own SQL variant and is not necessarily compatible with the Oracle SQL engine that you ultimately want to process your query Queries are routinely parsed and reconstructed so the JET engine can understand them Therefore, the Oracle SQL you have created may look... Therefore, the Oracle SQL you have created may look nothing like the query that is submitted to Oracle OO4O does not contain a SQL engine, and as a rule, does not reconstruct the queries provided to it The OO4O model is to pass the query to Oracle, let Oracle parse it, and then ask Oracle for the query description Oracle SQL and PL/SQL allow for the embedding of bind variables (parameters), which enables... tight integration with Oracle7 make it a very powerful interface you should thoroughly consider when choosing a database connectivity layer Previous TOC Page Next Page Home Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Previous TOC Page q Next Page Home 48 r The Oracle Data Control s Understanding ODC s What Is a VBX? s What Type of VBX Is the Oracle Data Control? s Reviewing... bound to it Understanding ODC Oracle Objects for OLE (OO4O) provides an OLE Server for programmatic development Because Visual Basic 3.0 is a popular environment and because data aware controls make development even easier, the Oracle Data Control is an excellent helper tool and logical addition to Oracle Objects for OLE The inclusion of the Oracle Data Control makes Oracle Objects for OLE a reasonable... (and possibly other applications) by adding functionality not contained in the original product What Type of VBX Is the Oracle Data Control? Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark The Oracle Data Control is a level III custom control Although the Oracle Data Control appears to be a data control, it is not The control development kit has no specification for writing... of the Oracle Data Control ("oradata1" by default) The form should resemble Figure 48.5 Figure 48.5 Oracle Data Control and TrueGrid on a form 1 Run the project (Run | Start) If you properly set the necessary properties of the Oracle Data Control and the TrueGrid, then rows and columns appear in the TrueGrid You can stop the application using Run | End Please purchase PDF Split-Merge on www.verypdf.com... purchase PDF Split-Merge on www.verypdf.com to remove this watermark update The product documentation lists a number of differences between the Oracle Data Control and the Microsoft data control as well as problems that some data aware controls have when trying to use the Oracle Data Control Migrating from the MS Data Control/ODBC to the ODC/OLE Server Moving from the Microsoft data control to the Oracle. .. done, and the Oracle Data Control does appear to work with a variety of popular controls The best advice is to test the Oracle Data Control with any data aware controls that your application may require, because compatibility is not guaranteed Previous TOC Page Next Page Home Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Previous TOC Page q Next Page Home 49 r Oracle Objects . changes at Oracle& apos;s discretion. Oracle Objects for OLE also is available as a 90-day trial product on Oracle& apos;s World Wide Web site at www .oracle. com Application Errors ■ Oracle Errors ■ Comparison with DAO/JET ■ Differences Between Oracle Objects and DAO ■ Oracle- Specific Features Please purchase PDF Split-Merge