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    "# Constituent Parsing Exercises\n",
    "\n",
    "\n",
    "\n",
    "In the lecture we took a look at a simple tokenizer and sentence segmenter. In this exercise we will expand our understanding of the problem by asking a few important questions, and looking at the problem from a different perspectives."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "##  <font color='green'>Setup 1</font>: Load Libraries"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
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   "source": [
    "%%capture\n",
    "%load_ext autoreload\n",
    "%autoreload 2\n",
    "%matplotlib inline\n",
    "# %cd .. \n",
    "import sys\n",
    "sys.path.append(\"..\")\n",
    "import math \n",
    "import statnlpbook.util as util\n",
    "import statnlpbook.parsing as parsing"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## <font color='blue'>Task 1</font>: Understanding parsing\n",
    "\n",
    "Be sure you understand [grammatical categories and structures](http://webdelprofesor.ula.ve/humanidades/azapata/materias/english_4/grammatical_categories_structures_and_syntactical_functions.pdf) and brush up on your [grammar skils](http://www.ucl.ac.uk/internet-grammar/intro/intro.htm).\n",
    "\n",
    "Then re-visit the [Enju online parser](http://www.nactem.ac.uk/enju/demo.html), and parse the following sentences...\n",
    "\n",
    "What is wrong with the parses of the following sentences? Are they correct?\n",
    "- Fat people eat accumulates.\n",
    "- The fat that people eat accumulates in their bodies.\n",
    "- The fat that people eat is accumulating in their bodies.\n",
    "\n",
    "What about these, is the problem in the parser or in the sentence?\n",
    "  - The old man the boat.\n",
    "  - The old people man the boat.  \n",
    "\n",
    "These were examples of garden path sentences, find out what that means.\n",
    "\n",
    "What about these sentences? Are their parses correct?\n",
    "  - Time flies like an arrow; fruit flies like a banana.\n",
    "  - We saw her duck."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## <font color='blue'>Task 2</font>: Parent Annotation\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Reminisce the lecture notes in parsing, and the mentioned parent annotation. (grand)*parents, matter - knowing who the parent is in a tree gives a bit of context information which can later help us with smoothing probabilities, and approaching context-dependent parsing.\n",
    "\n",
    "in that case, each non-terminal node should know it's parent. We'll do this exercise on a single tree, just to play around a bit with trees and their labeling.\n",
    "\n",
    "\n",
    "Given the following tree:"
   ]
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  {
   "cell_type": "code",
   "execution_count": 2,
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   "outputs": [
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    "x = ('S', [('Subj', ['He']), ('VP', [('Verb', ['shot']), ('Obj', ['the', 'elephant']), ('PP', ['in', 'his', 'pyjamas'])])])\n",
    "parsing.render_tree(x)"
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    "Construct an `annotate_parents` function which will take that tree, and annotate its parents. The final annotation result should look like this:"
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     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "y = ('S^?', [('Subj^S', ['He']), ('VP^S', [('Verb^VP', ['shot']), ('Obj^VP', ['the', 'elephant']), ('PP^VP', ['in', 'his', 'pyjamas'])])])\n",
    "parsing.render_tree(y)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Solutions\n",
    "\n",
    "You can find the solutions to this exercises [here](parsing_solutions.ipynb)"
   ]
  }
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