Capítulo I. UNIVERSIDAD, EDUCACIÓN Y TURISMO
I.2. Pensar la educación superior universitaria
I.2.3. La educación superior y las competencias profesionales
Figure 7 on page 39 shows the CrossAccess architecture, which consists of the following major components:
• CrossAccess Data Server:
CrossAccess data server is responsible for all data access. It performs the following functions:
• Accepting SQL queries from ODBC clients or the sample applications (CXASAMP).
• Determining the type of data to be accessed.
• Rewriting the SQL query into the native file or database access language needed. A single SQL access could translate into multiple native requests.
• Optimizing queries based on generic SQL query rewrite and file—or database-specific optimization.
• Querying multiple data sources for JOINs.
• Translating result sets into a consistent relational format, which involves restructuring non-relational data into columns and rows. • Sorting result sets as needed; such as ORDER BY.
• Issuing all client catalog queries to the CrossAccess meta data catalog. • Stored procedure interface, which allows an Assembler, COBOL, or PLI
application program to be invoked.
The following components run on the data server:
Region Controller Services—This data server component is responsible for starting, stopping, and monitoring all of the other components of the data server. It determines which services to start based on SERVICE INFO ENTRY parameters in the Data Server Master configuration file. Initialization Services—This data server component is responsible for initializing and terminating different types of interfaces to underlying
database management systems or systems components such as Language Environment (LE) or WLM initialization service.
Connection Handler Services—This data server component is responsible for listening for connection requests from ODBC clients. Connection requests are routed to the appropriate query processor task for subsequent processing.
Query Processor Services—This data server component is responsible for translating client SQL into database and file-specific data access
requests.
Logger Services—This data serve component is used for system monitoring and trouble shooting. A single logger task can be running within a data server. During normal operations, you will not be concerned with the logger service.
• Enterprise Server:
The Enterprise Server is an optional component that you can use to manage a large number of concurrent users across multiple data sources (see Figure 8 on page 40). Like a data server, the Enterprise Server’s connection handler is responsible for listening for client connection requests. However, when a connection request is received, the Enterprise Server does not forward the request to a query processor task for
processing. Instead, the connection request is forwarded to a data source handler (DSH) and then to a Data Server for processing. The Enterprise Server maintains the end-to-end connection between the client application and the target data server. It is responsible for sending and receiving messages between the client application and the data server.
The Enterprise Server determines the locations of the data servers that it will be communicating with through the configuration parameters. Also, it determines whether those data servers are running on the same platform as the Enterprise Server.
The Enterprise Server can automatically start a local Data Server if there are no instances active. It can also start additional instances of a local data server when the currently active instances have reached the maximum number of concurrent users they can service, or the currently active instances are all busy.
• Data Mapper:
The CrossAccess nonrelational Data Mapper is a Microsoft
Windows-based application that automates many of the tasks required to create logical table definitions for nonrelational data structures. The Data
Mapper interprets existing physical data definitions that define both the content and the structure of nonrelational data.
The Data Mapper accomplishes the creation of logical table definitions for nonrelational data structures by creating meta data grammar from existing nonrelational data definitions. The meta data grammar is used as input to the CrossAccess meta data utility to create a meta data catalog that defines how the nonrelational data structure is mapped to an equivalent logical table. The meta data catalogs are used by query processor tasks to facilitate both the access and translation of the data from the nonrelational data structure into relational result sets.
The Data Mapper import utilities create initial logical tables from COBOL copybooks. A visual point-and-click environment is used to refine these initial logical tables to match site- and user-specific requirements. You can utilize the initial table definitions automatically created by Data Mapper, or customize those definitions as needed.
It is possible to create multiple logical tables that map to a single physical file or database. With this facility you can customize these table definitions to the needs of the user. Figure 9 on page 41 shows the Data Mapper workflow.
• Client Interface Module:
The client interface module is used to establish and maintain connections with Data Servers and Enterprise Servers. It performs the following functions:
• Determines and loads the appropriate transport layer module, based on configuration parameters
• Establishes communications with Data Servers and Enterprise Servers • De-references host variables in SQL statements
• Stores and retrieves data in the application storage areas • Presents error and feedback information to the application
The Client Interface Module can establish multiple connections to a Data Server or Enterprise server on behalf of a single application program.
Figure 7. CrossAccess Architecture
Sample Application (CXASAMP) with client interface module
Region Controller Tasks
CrossAccess Data Server MVS or VSE
Operator Logger tasks
Connection Handler Multiple Query Processor System Exits Transport layer • TCP/IP • SNA LU6.2 • Cross Memory
ODBC Application CrossAccess ODBC Client Windows Workstation DL/I DATA VSAM DATA SSIs Meta Data Catalogs
Figure 8. CrossAccess Architecture with Enterprise Server MVSor VSE DL/I DATA VSAM DATA MVS or VSE CrossAccess Enterprise Server CrossAccess Data Server Meta Data Catalogs CrossAccess Data Server CrossAccess Data Server ODBC Application CrossAccess ODBC Client
Figure 9. CrossAccess Data Mapper Workflow
PC
SERVER
File Definition Source
Step 3:
Generate Meta data grammar
Step 2: Customize Target Database Definition File Definition Source Meta Data Catalogs
*
Meta Data UtilityStep 1: Import data descriptions DBDs or COBOL copybooks Meta Data Grammar DataMapper Step 4: Export Meta Data
*
SYSIBM.SYSTABLES SYSIBM.SYSCOLUMNS SYSIBM.SYSINDEXES SYSIBM.SYSKEYS SYSIBM.SYSTABAUTHThe Data Mapper contains embedded FTP support to facilitate file transfer from and to the mainframe.