Once in a while clients need to expose data from a custom build data store to their xMII Server, this article describes the best practices for doing that. This article is also intended to support the 2.5.x and 4.0.x xMII UDSs and will most likely be supported in future connectivity products. Though a custom xMII UDS can be developed (through negotiations with solution management), but the cost and schedule can make it OPC DA, OPC HDA and OLE DB. OPC is standards organization that is "dedicated to interoperability in automation". Although OPC has several standards we will focus on the ones that are currently accessible to the current line of xMII connectivity products. OPC Data Access, or simply OPC DA, is probably the most recognized and implemented set to standards in the OPC portfolio. OPC DA exposes current values as well as allows for writing values to the items (OPC uses the generic term 'item' were other automation vendors use the term 'tag', for this article I'll use the term 'item'). The namespace is also exposed so that other systems can see what information is on the server, xMII will use this data to create query templates, and though the OPC DA specification may say it is 'optional' but it is required by the xMII UDS, so implement it. The OPC DA specification 2.05A specification is supported by the 2.5.x and 4.0.x versions of the xMII UDSs, the 4.0.x xMII UDSs also supports the 3.0 version of the OPC DA specification. It should be noted that the 1.0 OPC specification is not supported by the xMII UDSs. Any future connectivity products will most likely support both OPC DA 2.05A and 3.00, but 1.0 will remain unsupported. OPC HDA, or OPC Historical Data Access, is another interface that can be used to connect to historical tag systems. Currently the xMII UDSs support the 1.20A revision of the interface only. The OPC HDA specification supports current and historical queries and writes, interpolated historical trends and statistical information, all of which can be accessed through the xMII OPC HDA UDS. Other interfaces are currently not exposed to the UDS for data retrieval. OLE DB is probably the oldest supported database access interface in the Microsoft realm. Though it is older then ODBC, it is generally the lowest level interface a database system will expose, and in some cases the most efficient. It should be noted that the queries to the database need not be SQL or any other relational language (though most vendors have defined a SQL like language). If retrieval of non time series data is required, the OLE DB interface is the recommended extraction approach. To summarize, if a client needs to access data in a custom or obscure data source into SAP xMII and that back end source is a Microsoft based operating system, then it is recommended that the parties involved create an interface to either OPC DA, OPC HDA or OLE DB, or a combination there of, to access this data. This will allow for the greatest integration with any future releases if xMII and the xMII UDSs.
