Process Flow is a very important component
of Oracle Warehouse Builder. With Process Flow, we can create and control the ETL process by setting all kinds
of activities in a well-constructed flow. In Oracle Warehouse Builder 11gR2, there are 28 kinds
of activities, which fall into three categories: Control activities, OWB specific activities and Utility activities. For more information about Process Flow activities, please refer to OWB online doc. Most
of those activities are pre-defined for some specific use. For example, the Mapping activity allows execution an OWB mapping in Process Flow and the FTP activity allows an interaction between the local host and a remote FTP server. Besides those activities for specific purposes, the User Defined activity enables you to incorporate into a Process Flow an activity that is not defined within Warehouse Builder. So the User Defined activity brings flexibility and extensibility to Process Flow. In this article, we will take an amazing tour
of using the User Defined activity. Let's start. Enable execution
of User Defined activity Let's start this section from creating a very simple Process Flow, which contains a Start activity, a User Defined activity and an End Success activity. Leave all parameters
of activity USER_DEFINED unchanged except that we enter /tmp/test.sh into the Value column
of the COMMAND parameter. Then let's create the shell script test.sh in /tmp directory. Here is the content
of /tmp/test.sh (this article is demonstrating a scenario in Linux system, and /tmp/test.sh is a Bash shell script): echo Hello World! > /tmp/test.txt Note: don't forget to grant the execution privilege on /tmp/test.sh to OS Oracle user. For simplicity, we just use the following command. chmod +x /tmp/test.sh OK, it's so simple that we’ve almost done it. Now deploy the Process Flow and run it. For a newly installed OWB, we will come across an error saying "RPE-02248: For security reasons, activity operator Shell has been disabled by the DBA". See below. That's because, by default, the User Defined activity is DISABLED. Configuration about this can be found in <ORACLE_HOME>/owb/bin/admin/Runtime.properties: property.RuntimePlatform.0.NativeExecution.Shell.security_constraint=DISABLED The property can be set to three different values: NATIVE_JAVA, SCHEDULER and DISBALED. Where NATIVE_JAVA uses the Java 'Runtime.exec' interface, SCHEDULER uses a DBMS Scheduler external job submitted by the Control Center repository owner which is executed by the default operating system user configured by the DBA. DISABLED prevents execution via these operators. We enable the execution
of User Defined activity by setting: property.RuntimePlatform.0.NativeExecution.Shell.security_constraint= NATIVE_JAVA Restart the Control Center service for the change
of setting to take effect. cd <ORACLE_HOME>/owb/rtp/sql sqlplus OWBSYS/<password
of OWBSYS> @stop_service.sql sqlplus OWBSYS/<password
of OWBSYS> @start_service.sql And then run the Process Flow again. We will see that the Process Flow completes successfully. The execution
of /tmp/test.sh successfully generated a file /tmp/test.txt, containing the line Hello World!.
Pass parameters to User Defined Activity The Process Flow created in the above section has a drawback: the User Defined activity doesn't accept any information from OWB nor does it give any meaningful results back to OWB. That's to say, it lacks interaction. Maybe, sometimes such a Process Flow can fulfill the business requirement. But for most
of the time, we need to get the User Defined activity executed according to some information prior to that step. In this section, we will see how to
pass parameters to the User Defined activity and
pass them into the to-be-executed shell script. First, let's see how to
pass parameters to the script. The User Defined activity has an input parameter named PARAMETER_LIST. This is a list
of parameters that will be passed to the command. Parameters are separated from one another by a token. The token is taken as the first character on the PARAMETER_LIST string, and the string must also end in that token. Warehouse Builder recommends the '?' character, but any character can be used. For example, to
pass 'abc,' 'def,' and 'ghi' you can use the following equivalent: ?abc?def?ghi? or !abc!def!ghi! or |abc|def|ghi| If the token character or '\' needs to be included as part
of the parameter, then it must be preceded with '\'. For example '\\'. If '\' is the token character, then '/' becomes the escape character. Let's configure the PARAMETER_LIST parameter as below: And modify the shell script /tmp/test.sh as below: echo $1 is saying hello to $2! > /tmp/test.txt Re-deploy the Process Flow and run it. We will see that the generated /tmp/test.txt contains the following line: Bob is saying hello to Alice! In the example above, the parameters passed into the shell script are static. This case is not so useful because: instead
of passing parameters, we can directly write the value
of the parameters in the shell script. To make the case more meaningful, we can
pass two dynamic parameters, that are obtained from the previous activity, to the shell script. Prepare the Process Flow as below: The Mapping activity MAPPING_1 has two output parameters: FROM_USER, TO_USER. The User Defined activity has two input parameters: FROM_USER, TO_USER. All the four parameters are
of String type. Additionally, the Process Flow has two string variables: VARIABLE_FOR_FROM_USER, VARIABLE_FOR_TO_USER. Through VARIABLE_FOR_FROM_USER, the input parameter FROM_USER
of USER_DEFINED gets value from output parameter FROM_USER
of MAPPING_1. We achieve this by binding both parameters to VARIABLE_FOR_FROM_USER. See the two figures below. In the same way, through VARIABLE_FOR_TO_USER, the input parameter TO_USER
of USER_DEFINED gets value from output parameter TO_USER
of MAPPING_1. Also, we need to change the PARAMETER_LIST
of the User Defined activity like below: Now, the shell script is getting input from the Mapping activity dynamically. Deploy the Process Flow and all
of its necessary dependees then run the Process Flow. We see that the generated /tmp/test.txt contains the following line: USER B is saying hello to USER A! 'USER B' and 'USER A' are two outputs
of the Mapping execution. Write the shell script within Oracle Warehouse Builder In the previous section, the shell script is located in the /tmp directory. But sometimes, when the shell script is small, or for the sake
of maintaining consistency, you may want to keep the shell script inside Oracle Warehouse Builder. We can achieve this by configuring these three parameters
of a User Defined activity properly: COMMAND: Set the path
of interpreter, by which the shell script will be interpreted. PARAMETER_LIST: Set it blank. SCRIPT: Enter the shell script content. Note that in Linux the shell script content is passed into the interpreter as standard input at runtime. About how to actually
pass parameters to the shell script, we can utilize variable substitutions. As in the following figure, ${FROM_USER} will be replaced by the value
of the FROM_USER input parameter
of the User Defined activity. So will the ${TO_USER} symbol. Besides the custom substitution variables, OWB also provide some system pre-defined substitution variables. You can refer to the online document for that. Deploy the Process Flow and run it. We see that the generated /tmp/test.txt contains the following line: USER B is saying hello to USER A! Leverage the return value
of User Defined activity All
of the previous sections are connecting the User Defined activity to END_SUCCESS with an unconditional transition. But what should we do if we want different subsequent activities for different shell script execution results? 1. The simplest way is to add three simple-conditioned out-going transitions for the User Defined activity just like the figure below. In the figure, to simplify the scenario, we connect the User Defined activity to three End activities. Basically, if the shell script ends successfully, the whole Process Flow will end at END_SUCCESS, otherwise, the whole Process Flow will end at END_ERROR (in our case, ending at END_WARNING seldom happens). In the real world, we can add more complex and meaningful subsequent business logic. 2. Or we can utilize complex conditions to work with different results
of the User Defined activity. Previously, in our script, we only have this line: echo ${FROM_USER} is saying hello to ${TO_USER}! > /tmp/test.txt We can add more logic in it and return different values accordingly. echo ${FROM_USER} is saying hello to ${TO_USER}! > /tmp/test.txt if CONDITION_1 ; then ...... exit 0 fi if CONDITION_2 ; then ...... exit 2 fi if CONDITION_3 ; then ...... exit 3 fi After that we can leverage the result by checking RESULT_CODE in condition expression
of those out-going transitions. Let's suppose that we have the Process Flow as the following graph (SUB_PROCESS_n stands for more different further processes): We can set complex condition for the transition from USER_DEFINED to SUB_PROCESS_1 like this: Other transitions can be set in the same way. Note that, in our shell script, we return 0, 2 and 3, but not 1. As in Linux system, if the shell script comes across a system error like IO error, the return value will be 1. We can explicitly handle such a return value. Summary Let's summarize what has been discussed in this article: How to create a Process Flow with a User Defined activity in it How to
pass parameters from the prior activity to the User Defined activity and finally into the shell script How to write the shell script within Oracle Warehouse Builder How to do variable substitutions How to let the User Defined activity return different values and in what way can we leverage
