diff --git a/plugins/sentiment140/__init__.py b/plugins/sentiment140/__init__.py
index 123bc73..caf38f1 100644
--- a/plugins/sentiment140/__init__.py
+++ b/plugins/sentiment140/__init__.py
@@ -35,8 +35,12 @@ class Sentiment140Plugin(SentimentPlugin):
             polarity = "marl:Positive"
         elif polarity_value < 50:
             polarity = "marl:Negative"
-        entry = Entry(text=params["input"])
-        opinion = Opinion(hasPolarity=polarity, polarityValue=polarity_value)
+        entry = Entry(text=params["input"],
+                      prefix=params.get("prefix", ""))
+        opinion = Opinion(hasPolarity=polarity,
+                          polarityValue=polarity_value,
+                          prefix=params.get("prefix", ""))
+        opinion["prov:wasGeneratedBy"] = self.id
         entry.opinions.append(opinion)
         entry.language = lang
         response.entries.append(entry)
diff --git a/senpy/blueprints.py b/senpy/blueprints.py
index cafc91d..0b781cb 100644
--- a/senpy/blueprints.py
+++ b/senpy/blueprints.py
@@ -48,7 +48,7 @@ def get_params(req, params=BASIC_PARAMS):
             if alias in indict:
                 outdict[param] = indict[alias]
         if param not in outdict:
-            if options.get("required", False):
+            if options.get("required", False) and "default" not in options:
                 wrong_params[param] = params[param]
             else:
                 if "default" in options:
diff --git a/senpy/context.jsonld b/senpy/context.jsonld
index 36a3cd8..936db98 100644
--- a/senpy/context.jsonld
+++ b/senpy/context.jsonld
@@ -34,6 +34,7 @@
         "@id": "dc:date",
         "@type": "xsd:dateTime"
     },
+    "text": { "@id": "nif:isString" },
     "wnaffect": "http://www.gsi.dit.upm.es/ontologies/wnaffect#",
     "xsd": "http://www.w3.org/2001/XMLSchema#"
 }
diff --git a/senpy/extensions.py b/senpy/extensions.py
index 5ee9ac0..14f3fb3 100644
--- a/senpy/extensions.py
+++ b/senpy/extensions.py
@@ -9,11 +9,6 @@ logger = logging.getLogger(__name__)
 
 from .plugins import SentimentPlugin, EmotionPlugin
 
-try:
-    from flask import _app_ctx_stack as stack
-except ImportError:
-    from flask import _request_ctx_stack as stack
-
 from .blueprints import nif_blueprint
 from git import Repo, InvalidGitRepositoryError
 
@@ -145,11 +140,9 @@ class Senpy(object):
     @property
     def plugins(self):
         """ Return the plugins registered for a given application.  """
-        ctx = stack.top
-        if ctx is not None:
-            if not hasattr(ctx, 'senpy_plugins') or self._outdated:
-                ctx.senpy_plugins = self._load_plugins()
-            return ctx.senpy_plugins
+        if not hasattr(self, 'senpy_plugins') or self._outdated:
+            self.senpy_plugins = self._load_plugins()
+        return self.senpy_plugins
 
     def filter_plugins(self, **kwargs):
         """ Filter plugins by different criteria """
diff --git a/senpy/models.py b/senpy/models.py
index 0d18290..dce3cbd 100644
--- a/senpy/models.py
+++ b/senpy/models.py
@@ -80,7 +80,6 @@ class Opinion(Leaf):
     opinionContext = {}
     def __init__(self, polarityValue=None, hasPolarity=None, *args, **kwargs):
         super(Opinion, self).__init__(context=self.opinionContext,
-                                      prefix="marl",
                                       *args,
                                       **kwargs)
         if polarityValue is not None:
@@ -95,7 +94,6 @@ class EmotionSet(Leaf):
         if not emotions:
             emotions = []
         super(EmotionSet, self).__init__(context=self.emotionContext,
-                                         prefix="onyx",
                                          *args,
                                          **kwargs)
         self.emotions = emotions or []
diff --git a/senpy/plugins.py b/senpy/plugins.py
index 31e80e2..6c3b73d 100644
--- a/senpy/plugins.py
+++ b/senpy/plugins.py
@@ -25,6 +25,10 @@ PARAMS = {"input": {"aliases": ["i", "input"],
                        "required": False,
                        "options": ["es", "en"],
                        },
+          "prefix": {"aliases": ["prefix", "p"],
+                     "required": True,
+                     "default": "",
+          },
           "urischeme": {"aliases": ["urischeme", "u"],
                         "required": False,
                         "default": "RFC5147String",
@@ -56,9 +60,13 @@ class SenpyPlugin(object):
     def disable(self):
         self.enabled = False
 
+    @property
+    def id(self):
+        return "{}_{}".format(self.name, self.version)
+
     def jsonable(self, parameters=False):
         resp = {
-            "@id": "{}_{}".format(self.name, self.version),
+            "@id": self.id,
             "enabled": self.enabled,
         }
         if hasattr(self, "repo") and self.repo: