I want to check the database in my app every 12 hrs for rows with date column having corresponding date. This is accomplished by writing service in android. But is there any equivalent of services in iOS so that my requirement can be accomplished?
No. There is no such thing in the SDK or in iPhone/iPad in general. You can only write code that will affect the eco system of the app, not the operating system. When your app is closed it's closed and no action will be taken until the user opens it/opens a push notification related to your app.
If the user approved location based services for your app, there are a few ways to run short background process even if your app is totally closed. One of them is by using Monitoring Shape-Based Regions which basically means if the user left region X/entered region Y open the app and run a few commands before closing it again.
The clever way (and the only way I can think of) to accomplish what you're after in iOS is to run that service on a server and pull the data from the server when the app is opened.
In iOS7 and later you can use background fetch for this task. You can check this tutorial: http://code.tutsplus.com/tutorials/ios-7-sdk-working-with-background-fetch--mobile-20520
You can find the solution here. Background Execution does this.
Added: Apple does not allow apps to run in background for all the time. It provides some finite-length time to complete your app execution. You can increase that time depending on your execution need. But that is not recommended.
来源：https://stackoverflow.com/questions/16667912/is-there-any-equivalent-of-services-of-android-in-ios