> # About SequeLink® Services and Data Sources

> SequeLink Server installs the following server software service components to provide data connectivity, performance, and administration for two-tier client/server and n-tier Web/application server environments:

> - SequeLink data access services handle data access requests from any SequeLink Client. Multiple SequeLink data access services can run on the same SequeLink Server. For example, SequeLink Server for Oracle and SequeLink Server for Microsoft SQL Server can run side-by-side on the same machine.
> - SequeLink Agent services carry out configuration, management, and monitoring requests from any SequeLink Manager. The SequeLink Agent can service multiple SequeLink services on the same SequeLink Server.

> When you complete the installation of the SequeLink Server software as documented in the SequeLink Installation Guide, a SequeLink data access service is configured for the type of SequeLink Server you installed (for example, SequeLink Server for Oracle). In addition, a SequeLink Agent is configured to handle configuration, management, and monitoring requests from any SequeLink Manager.

> ### Data Sources

> SequeLink uses two types of data sources-server data sources and client data sources.

> #### Server Data Sources

> Server data sources are data sources configured on the SequeLink Server. These data sources contain settings that affect how the SequeLink service operates and settings that affect how data is accessed by SequeLink Clients. Centralizing this information on the server, instead of distributing it among hundreds of SequeLink Clients, provides easier management of your entire data access infrastructure. When you install SequeLink Server, a default server data source, named Default, is automatically created on the server, using the values you specified during installation. If necessary, you can modify the definition of the default server data source. Server data sources apply to a SequeLink service. Each SequeLink service can have multiple server data sources.

> Unlike server data sources, client data sources are minimal data sources configured on the SequeLink Client that contain connection instructions to a SequeLink data access service. The data access functionality of a session is governed by a set of data source and service attributes for the SequeLink data access service. These attributes are configured on the server.

> If you do not specify a server data source for your connection, the attributes of the Default server data source govern the data access functionality of the connection. For example, if you configured two server data sources named DS1 and DS2 as shown in Figure 1-2, and configured a SequeLink Client that did not specify a particular server data source, the data access functionality of the connection between the SequeLink Client and the SequeLink Server would be governed by the Default server data source.

> Figure 1-2. SequeLink Clients Specifying Server Data Sources

> Server data sources use SequeLink service attributes to define functionality. For example, if you set DataSourceReadOnly=Select, the client application will only be able to perform Select statements when using that service.

> NOTES:

> - SequeLink service attributes beginning with "DataSource", such as DataSourceReadOnly, are server data source attributes. Server data source attributes are always dynamic.
> - SequeLink Agent services do not have server data source attributes.

> Only commonly used service attributes are included in the default configuration of a SequeLink service. To configure other attributes, you must add that attribute explicitly to your SequeLink configuration.

> For instructions on configuring server data sources using the:

> - SequeLink Manager MMC Snap-in, see "Configuring SequeLink® Services Using the SequeLink Manager Snap-in".
> - SequeLink Manager Command-Line Tool, see "Using the SequeLink® Manager Command-Line Administrator".
> - SequeLink Manager for z/OS, see "Configuring SequeLink® Services Using the SequeLink® Manager for z/OS".

> #### Client Data Sources

> Client data sources are minimal data source containing the host, port, and server data source, that are configured on the SequeLink Client and provide connection instructions to a SequeLink data access service. When a client application connects to a SequeLink data access service using a SequeLink Client, the data access functionality of the session is governed by a set of data source and service attributes for the SequeLink data access service. These attributes are configured on the server. These attributes are configured on the server.

> Client data sources are required when configuring the SequeLink Client for ODBC or the SequeLink Client for ADO. For SequeLink Client for JDBC, you can configure either a client data source or a connection URL. SequeLink Client for .NET clients do not require a client data source; instead, you configure a connection string.

> See the following chapters for instructions on configuring client data sources for the SequeLink Client for ODBC and SequeLink Client for ADO Client:

> - "Configuring the ODBC Client"
> - "Configuring the ADO Client"

> See "Specifying JDBC Driver Connection URLs" for instructions on specifying connection URLs for SequeLink Client for JDBC. Configuring JDBC client data sources is considered an advanced topic.

> See "Specifying Connection Properties" for instructions on specifying connection options for the SequeLink Client for .NET.

> ### Service Attributes

> When a client application connects to a SequeLink data access service using a SequeLink Client, the data access functionality of the session is governed by a set of service and data source attributes for the SequeLink data access service.

> When you create a SequeLink service, only commonly used service attributes are included in the default configuration of a SequeLink service. The newly created SequeLink service contains a default server data source called Default, which is configured with the default values entered during installation.

> To configure other service or data source attributes, you must add each attribute explicitly to your SequeLink configuration. You configure SequeLink services and their attributes using the SequeLink Manager.

> SequeLink service attributes beginning with Service, such as ServiceCodePageMap, are SequeLink data access service attributes that are associated with a server data source. SequeLink service attributes beginning with "DataSource," such as DataSourceReadOnly, are SequeLink data access service attributes that are associated with a server data source.

> SequeLink service attributes are static or dynamic:

> - Static attributes require you to restart a SequeLink service when you add or change the attribute before the change becomes effective.
> - Dynamic attributes become effective after the attribute is added or changed and the configuration is saved. Most dynamic attributes affect the behavior of a database connection; therefore, when you add or change an attribute, the new values are used for the next connection. Active connections do not use the new values.

> See "SequeLink® Service Attributes" for a complete list and description of SequeLink service attributes.

> ### SequeLink® Service Templates

> When you install SequeLink Server, at least one SequeLink data access service is installed using default attributes for that service. Default service attributes are defined in the SequeLink service templates. Using the SequeLink Manager, you can create additional services based on the SequeLink service templates. Examples of SequeLink service templates include:

> - [SequeLink 6.0] Agent Service
> - [SequeLink 6.0] DB2 for LUW service
> - [SequeLink 6.0] DB2 for z/OS service
> - [SequeLink 6.0] Informix service
> - [SequeLink 6.0] JDBC Socket service
> - [SequeLink 6.0] ODBC Socket service
> - [SequeLink 6.0] Oracle 10 service
> - [SequeLink 6.0] SQL Server service
> - [SequeLink 6.0] Sybase service

> See "Creating a SequeLink® Service" for information on creating a SequeLink service and a complete list of SequeLink service templates.

> ### Monitoring SequeLink® Service Activity

> SequeLink can monitor services, sessions, statements, and data access events. To configure what you want SequeLink to monitor, you can use the SequeLink Manager. For information about setting monitoring profiles using the:

> - SequeLink Manager Snap-in, see "Configuring SequeLink® Services Using the SequeLink Manager Snap-in".
> - SequeLink Manager Command-Line Tool, see "Using the SequeLink® Manager Command-Line Administrator".
> - SequeLink Manager for z/OS, see "Configuring SequeLink® Services Using the SequeLink® Manager for z/OS".

> You can integrate SequeLink monitoring with the Windows Performance Monitor tool, which allows you to access monitoring information from this Windows tool. See "Integrating SequeLink® Monitoring with the Windows Performance Tool" for instructions on integrating SequeLink monitoring with the Windows Performance Monitor tool.

> ### Event Handling

> All important server actions, such as data access activity and stopping and starting the server, cause an event to be generated. Depending on which SequeLink profiles are active, the information generated by the event is displayed as it occurs on the runtime monitor and stored in a file named the event trace file. By default, the event trace file is located in the installdir/tracing directory, where installdir is your SequeLink Server installation directory.

> By setting profiles in your SequeLink service configuration to control which events are traced, you can inspect information generated by these events. Event tracing allows you to monitor ongoing activity, troubleshoot problems, and fine-tune your data access infrastructure. For example, if you want to monitor the number of transactions a SequeLink Server processes for capacity planning purposes, you could set a profile in the SequeLink service configuration to return only that information. In addition, the information stored in the event trace file is persisted, meaning that you can inspect the information at a later time.

> Events are identified by:

> - An event ID
> - The service in which the event occurred
> - The time the event occurred
> - List of attributes and their values

> Examples of information that can be monitored and traced are SQL statements, number of transactions, failures, and authentication information.

> See "Configuring Event Tracing" for instructions on configuring the events to be monitored and traced by the SequeLink Manager.