First error: sObject type 'sObject' is not supported. If you are attempting to use a custom object, be sure to append the '__c' after the entity name.

hi sushant

there will be some correction in your code you need to specify your sobject  because it create some ambiguity becz

a.name can be either auto number or string so its create a situation which throws error. so if you wanted to update some fields of your object using batch you can call another batch class in ur class.

you can do something like this

global class SearchAndReplace implements Database.Batchable<sobject>{
global String Query;
global List<id>allObjIds ;
global SearchAndReplace(List<id>allObjectIds){
allObjIds=allObjectIds;
}
global Database.QueryLocator Start(Database.BatchableContext BC){
query='SELECT Id,Name FROM Account WHERE Id in:allObjIds';
return Database.getQueryLocator(query);
}
global void execute (Database.BatchableContext BC,List<Account>scope){
for(Account obj:scope){
obj.Name='Algoworks';
}
update scope;
}
global void finish (Database.BatchableContext BC){
SearchAndReplaceContact objc = new SearchAndReplaceContact(allObjIds);

}

another class get called inside above class

global class SearchAndReplaceContact implements Database.Batchable<sobject> {
global String Query;
global List<id>allObjIds ;
global SearchAndReplaceContact(List<id>allObjectIds){
allObjIds=allObjectIds;
}
global Database.QueryLocator Start(Database.BatchableContext BC){
query='SELECT Id,Name FROM Contact WHERE Id in:allObjIds';
return Database.getQueryLocator(query);
}
global void execute (Database.BatchableContext BC,List<Contact>scope){
for(Contact obj:scope){
obj.lastname='Algoworks';
}
update scope;
}
global void finish (Database.BatchableContext BC){
}

}