In hierarchical data, deferred loading techniques are employed to optimize performance by loading related data only when necessary, minimizing the amount of data retrieved from the database at once.

To implement a custom conflict resolution strategy in an ADO.NET application, you should handle the RowUpdating event. This event occurs before changes are sent to the database during an Update operation. By handling this event, you can examine the changes being made and implement your custom logic to resolve conflicts before they are applied to the database.

In LINQ to DataSet, the join clause is used to combine data from two or more data sources based on a related column between them. It allows you to perform operations similar to SQL joins, such as inner joins, outer joins, and cross joins, to retrieve and process data from multiple tables or collections simultaneously. Understanding how to use the join clause effectively is essential for querying and manipulating data using LINQ to DataSet.

In LINQ to DataSet, the GroupBy clause is used to group records based on a specified key. By grouping sales data by product category, you can then calculate the total revenue for each category. Thus, using GroupBy followed by an aggregation function like Sum allows you to achieve the task of calculating total revenue for each product category.

When interacting with an Oracle database in .NET applications, the appropriate data reader to use is the OracleDataReader. This specialized data reader is designed specifically for working with Oracle databases, providing efficient access to query results and handling Oracle-specific data types and features. Using the correct data reader ensures compatibility and optimal performance when retrieving data from an Oracle database.

Improving the performance of LINQ queries with multiple joins and filtering conditions involves using appropriate indexes on columns involved in joins and filters. This helps in optimizing data retrieval and processing, resulting in better query performance.

The primary benefits of using DataRelations when working with hierarchical data include simplifying navigation between related rows. DataRelations provide a convenient way to access child rows associated with a parent row, improving code readability and maintainability.

You can populate a DataTable with data from a database using the Fill method of a DataAdapter. It retrieves data from the database and populates the DataTable with the result set.

Deferred execution in LINQ to DataSet indicates that the query is not executed until you enumerate the results explicitly using methods like ToList(), ToArray(), or iterating through the query results. This postpones query execution until the data is actually needed.

The DataAdapter class in ADO.NET is responsible for transferring data between a data source, such as a database, and a data-bound control, such as a DataGridView or ListBox. It acts as a bridge between the data source and the dataset, facilitating the retrieval and manipulation of data.