Subtype dependency on corresponding subtypes

Hi All,

I have a design question.

I am writing an application that will search through the contents of
various files against a given search criteria. I envisage that there
will be different search strategies, each of which have different
search criteria. A couple of examples would be as per below.

Plain Text Strategy. Criteria: a single string (search term), case
sensitive flag.
Regular Expression Strategy: a single regular expression, number of
lines before and after each result to include, case sensitive flag.
XML Strategy: a single string (search term), name of the xml element
to be searched within.

I envisage having an abstract search type and concrete subclasses
based on each strategy. For example:

public interface Search {
   SearchResult search(SearchCriteria criteria);
}

public class PlainTextSearchStrategy implements Search {
   public SearchResult search(SearchCriteria criteria) {
      // do the search..
   }
}

public class RegularExpressionSearchStrategy implements Search
{ ... }

public class XmlSearchStrategy implements Search { ... }

My difficulty is the SearchCriteria. Each search strategy type would
have its own search criteria type and I do not think there is any
common behaviour (or data) that can be defined in the criteria super
type. As such, SearchCriteria is just a marker interface, and this
bothers me. The search strategy sub-types would need to cast
SearchCriteria to the specific type they need, so there is no type
safety beyond ensuring the marker interface is implemented. For
example:

public class PlainTextSearchStrategy implements Search {
   public SearchResult search(SearchCriteria criteria) {
      PlainTextSearchCriteria ptCriteria = (PlainTextSearchCriteria)
criteria;
      // do the search..
   }
}

Is there a design better suited to this problem of ensuring a sub-type
can rely on corresponding subtypes being present? As I understand it,
generics won't help me here either. Do I need to live with the
casting?

Any advice would be much appreciated!

Rob
:)