recognize and parse Schema.org Markup

src/com/dom_distiller/client/SchemaOrgParser.java

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package com.dom_distiller.client;
+
+import java.util.ArrayList;
+import java.util.EnumMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import com.google.gwt.dom.client.AnchorElement;
+import com.google.gwt.dom.client.Element;
+import com.google.gwt.dom.client.ImageElement;
+import com.google.gwt.dom.client.MetaElement;
+import com.google.gwt.dom.client.NodeList;
+
+/**
+ * This class recognizes and parses Schema.org markup tags, and returns the properties that matter
+ * to distilled content.
+ * For the basic Schema.org Thing type, the basic properties are: name, url, description, image.
+ * In addition, for each type that we support, we also parse more specific properties:
+ * - Article: headline (i.e. title), publisher, copyright year, copyright holder, date published,
+ *            date modified, author, article section
+ * - ImageObject: headline (i.e. title), publisher, copyright year, copyright holder, content url,
+ *                encoding format, caption, representative of page, width, height
+ * - Person: family name, given name
+ * - Organization: legal name.
+ * The value of a Schema.Org property can be a Schema.Org type, i.e. embedded.  E.g., the author or
+ * publisher of article or publisher of image could be a Schema.Org Person or Organization type;
+ * in fact, this is the reason we support Person and Organization types.
+ */
+public class SchemaOrgParser implements MarkupParser.Parser {
+    private static final String NAME_PROP = "name";
+    private static final String URL_PROP = "url";
+    private static final String DESCRIPTION_PROP = "description";
+    private static final String IMAGE_PROP = "image";
+    private static final String HEADLINE_PROP = "headline";
+    private static final String PUBLISHER_PROP = "publisher";
+    private static final String COPYRIGHT_HOLDER_PROP = "copyrightHolder";
+    private static final String COPYRIGHT_YEAR_PROP = "copyrightYear";
+    private static final String CONTENT_URL_PROP = "contentUrl";
+    private static final String ENCODING_FORMAT_PROP = "encodingFormat";
+    private static final String CAPTION_PROP = "caption";
+    private static final String REPRESENTATIVE_PROP = "representativeOfPage";
+    private static final String WIDTH_PROP = "width";
+    private static final String HEIGHT_PROP = "height";
+    private static final String DATE_PUBLISHED_PROP = "datePublished";
+    private static final String DATE_MODIFIED_PROP = "dateModified";
+    private static final String AUTHOR_PROP = "author";
+    private static final String SECTION_PROP = "articleSection";
+    private static final String FAMILY_NAME_PROP = "familyName";
+    private static final String GIVEN_NAME_PROP = "givenName";
+    private static final String LEGAL_NAME_PROP = "legalName";
+
+    private enum Type {  // All these types are extended from Thing, directly or indirectly.
+        IMAGE,
+        ARTICLE,
+        PERSON,
+        ORGANIZATION,
+        UNSUPPORTED,
+    }
+
+    private static class ThingItem {
+        protected final Type mType;
+        protected final Element mRoot;
+        protected final String[] mStringPropertyNames;
+        protected final String[] mItemPropertyNames;
+        protected final String[] mStringProperties;
+        protected final ThingItem[] mItemProperties;
+
+        protected ThingItem(Type type, Element root,
+                            String[] stringPropertyNames, String[] itemPropertyNames) {
+            mType = type;
+            mRoot = root;
+            mStringPropertyNames = stringPropertyNames;
+            mItemPropertyNames = itemPropertyNames;
+            mStringProperties = new String[mStringPropertyNames.length];
+            mItemProperties = new ThingItem[mItemPropertyNames.length];
+        }
+
+        protected String toStringProperty() {
+            return "";
+        }
+
+        protected MarkupParser.Image getImage() {
+            // Use value of IMAGE_PROP to create a MarkupParser.Image.
+            String imageUrl = getStringProperty(IMAGE_PROP);
+            if (imageUrl.isEmpty()) return null;
+            MarkupParser.Image image = new MarkupParser.Image();
+            image.image = imageUrl;
+            image.url = imageUrl;
+            return image;
+        }
+
+        protected MarkupParser.Article getArticle() {
+            return null;
+        }
+
+        protected final boolean isImageRepresentativeOfPage() {
+            String value = getStringProperty(REPRESENTATIVE_PROP);
+            return value.equalsIgnoreCase("true");
+        }
+
+        protected final void putStringValue(String name, String value) {
+            for (int i = 0; i < mStringPropertyNames.length; i++) {
+                if (name.equals(mStringPropertyNames[i])) {
+                    mStringProperties[i] = value;
+                    break;
+                }
+            }
+        }
+
+        protected final void putItemValue(String name, ThingItem value) {
+            for (int i = 0; i < mItemPropertyNames.length; i++) {
+                if (name.equals(mItemPropertyNames[i])) {
+                    mItemProperties[i] = value;
+                    break;
+                }
+            }
+        }
+
+        protected final String getStringProperty(String name) {
+            // Check if property exists in |mStringProperties|.
+            for (int i = 0; i < mStringPropertyNames.length; i++) {
+                if (name.equals(mStringPropertyNames[i])) {
+                    String value = mStringProperties[i];
+                    if (value != null && !value.isEmpty()) return value;
+                    break;
+                }
+            }
+            // Otherwise, repeat for |mItemProperties|.
+            for (int i = 0; i < mItemPropertyNames.length; i++) {
+                if (!name.equals(mItemPropertyNames[i])) continue;
+                if (mItemProperties[i] != null) return mItemProperties[i].toStringProperty();
+                break;
+            }
+            return "";
+        }
+    }
+
+    private final List<ThingItem> mItemScopes;
+    private Element mRoot = null;
+    private final Map<Type, String> mTypeUrls = new EnumMap<Type, String>(Type.class);

[cjhopman, 2014/04/17 17:35:26]

This appears to only be used to lookup a type for a string, so it should
probably be a Map<String, Type>

[kuan, 2014/04/18 00:19:03]

Done.

+
+    /**
+     * The object that extracts and verifies Schema.org markup tags from |root|.
+     */
+    public SchemaOrgParser(Element root) {
+        mRoot = root;
+        mItemScopes = new ArrayList<ThingItem>();
+
+        mTypeUrls.put(Type.IMAGE, "http://schema.org/ImageObject");
+        mTypeUrls.put(Type.ARTICLE, "http://schema.org/Article");
+        mTypeUrls.put(Type.PERSON, "http://schema.org/Person");
+        mTypeUrls.put(Type.ORGANIZATION, "http://schema.org/Organization");
+        mTypeUrls.put(Type.UNSUPPORTED, "");
+
+        // TODO(kuan): Parsing all tags is pretty expensive, should we do so only lazily?
+        // If parse lazily, all get* methods will need to check for parsed state and, if necessary,
+        // parse before returning the requested properties.
+        parseRoot();
+    }
+
+    @Override
+    public String getTitle() {
+        String title = findStringProperty(HEADLINE_PROP);
+        if (title.isEmpty()) title = findStringProperty(NAME_PROP);
+        return title;
+    }
+
+    @Override
+    public String getType() {
+        if (mItemScopes.isEmpty()) return null;
+        // Assume the type of the first item is the page type.
+        return mItemScopes.get(0).mType.toString();
+    }
+
+    @Override
+    public String getUrl() {
+        return findStringProperty(URL_PROP);
+    }
+
+    @Override
+    public MarkupParser.Image[] getImages() {
+        if (mItemScopes.isEmpty()) return null;
+        List<MarkupParser.Image> images = new ArrayList<MarkupParser.Image>();
+        for (int i = 0; i < mItemScopes.size(); i++) {
+            ThingItem item = mItemScopes.get(i);
+            MarkupParser.Image image = item.getImage();
+            if (image != null) {
+                if (item.isImageRepresentativeOfPage()) {
+                    // Image should be the dominant, i.e. first, one.
+                    images.add(0, image);
+                } else {
+                    images.add(image);
+                }
+            }
+        }
+        if (images.isEmpty()) return null;
+        return images.toArray(new MarkupParser.Image[images.size()]);
+    }
+
+    @Override
+    public String getDescription() {
+        return findStringProperty(DESCRIPTION_PROP);
+    }
+
+    @Override
+    public String getPublisher() {
+        return findStringProperty(PUBLISHER_PROP);
+    }
+
+    @Override
+    public String getCopyright() {
+        if (mItemScopes.isEmpty()) return "";
+        // Returns a concatenated string of copyright year and copyright holder of the first item
+        // that has these properties, delimited by a whitespace.
+        String copyright = "";
+        for (int i = 0; i < mItemScopes.size() && copyright.isEmpty(); i++) {
+            ThingItem item = mItemScopes.get(i);
+            copyright = concat(item.getStringProperty(COPYRIGHT_YEAR_PROP),
+                               item.getStringProperty(COPYRIGHT_HOLDER_PROP));
+        }
+        return copyright.isEmpty() ? copyright : "Copyright " + copyright;
+    }
+
+    @Override
+    public String getAuthor() {
+        return findStringProperty(AUTHOR_PROP);
+    }
+
+    @Override
+    public MarkupParser.Article getArticle() {
+        if (mItemScopes.isEmpty()) return null;
+        // Returns the first article.
+        MarkupParser.Article article = null;
+        for (int i = 0; i < mItemScopes.size() && article == null; i++) {
+            article = mItemScopes.get(i).getArticle();
+        }
+        return article;
+    }
+
+    @Override
+    public boolean optOut() {
+        return false;
+    }
+
+    private void parseRoot() {
+        // The <html> element can also be the start of a Schema.org item, and hence needs to be
+        // parsed.
+
+        // Use a boolean array for |skipChildren|, instead of the boolean primitive, so that it
+        // can be updated in checkIfElementIsSupported().
+        boolean[] skipChildren = new boolean[] { false };
+        checkIfElementIsSupported(mRoot, skipChildren);
+        if (skipChildren[0]) return;  // Skipping children of root means there's nothing more to do.
+        // Recursively parse each element that is an Schema.org type.
+        parse(mRoot, null);
+    }
+
+    private void parse(Element root, ThingItem currItem) {

[cjhopman, 2014/04/17 17:35:26]

This function and its uses will be simplified if currItem is the closest
ancestor item of the element passed in. (I.e. it is never the item started at
the element passed in). 

[kuan, 2014/04/18 00:19:03]

Done.

+        NodeList<Element> allElems = root.getElementsByTagName("*");
+        for (int i = 0; i < allElems.getLength(); i++) {

[cjhopman, 2014/04/17 17:35:26]

The way that the tree is parsed is hard for me to follow. Why not walk the tree
recursively rather than iterating over all the elements? (The current approach
also has bad worst case behavior)

[kuan, 2014/04/18 00:19:03]

Done.  what's the worst case behavior?

[cjhopman, 2014/04/18 01:17:01]

The previous version had O(n^2) worst case complexity (this would happen if you
had a bunch of nested elements with each one starting a new nested item).

+            Element e = allElems.getItem(i);
+            // See comments in parseRoot() for using boolean array for |skipChildren|.
+            boolean[] skipChildren = new boolean[] { false };
+
+            ThingItem newItem = checkIfElementIsSupported(e, skipChildren);
+
+            // If we're currently parsing a Schema.org type, if it has an "itemprop" attribute that
+            // we care for, extract and store its value.
+            if (currItem != null) extractProperty(e, currItem, newItem);
+
+            // If current element has "itemscope" and "itemtype" attributes and is a supported type,
+            // its children would have been parsed by |newItem| via the recursive parse() call.
+            // If it's an unsupported type, its children should be ignored.  In both cases, we
+            // should skip these children to the next sibling of the current element.  So, determine
+            // the index of the next sibiling in |allElems|, so that the next iteration will jump to
+            // that element.
+            if (skipChildren[0]) {
+                Element next = e.getNextSiblingElement();
+                if (next != null) {
+                    for (i++; i < allElems.getLength() && next != allElems.getItem(i); i++) {}
+                    i--;  // Decrement because it'll be incremented in the outer for loop.
+                } else {
+                    break;  // No next sibling means there's no more elements to process.
+                }
+            }
+        }  // for all elements
+    }
+
+    // If |e| has "itemscope" and "itemtype" attributes and a supported type, a ThingItem-extended
+    // object is created based on the type.
+    // Returns this object after it has recursively parsed |e|'s children, returns null otherwise.
+    // @param skipChildren[0] is set to true if |e| specifies a Schema.org type, supported or not.
+    private ThingItem checkIfElementIsSupported(Element e, boolean[] skipChildren) {
+         // If element has "itemscope" and "itemtype" attributes, it's the start of an item.
+         // If the type is what we care for, instantiate the corresponding extended ThingItem and
+         // recursively parse it.
+        if (!e.hasAttribute("ITEMSCOPE") || !e.hasAttribute("ITEMTYPE")) return null;

[cjhopman, 2014/04/17 17:35:26]

This should be a different function so you don't have to pass around a
one-element boolean array to get the result of this check.

[kuan, 2014/04/18 00:19:03]

Done.

+
+        skipChildren[0] = true;  // Indicate to skip the children of this supported element.
+        ThingItem newItem = null;
+        Type type = getType(e);
+        switch (type) {
+            case IMAGE:
+                newItem = new ImageItem(e);
+                break;
+            case ARTICLE:
+                newItem = new ArticleItem(e);
+                break;
+            case PERSON:
+                newItem = new PersonItem(e);
+                break;
+            case ORGANIZATION:
+                newItem = new OrganizationItem(e);
+                break;
+            case UNSUPPORTED:
+            default:
+                return null;
+        }
+
+        mItemScopes.add(newItem);
+        parse(e, newItem);

[cjhopman, 2014/04/17 17:35:26]

This parse() call makes it harder for me to reason about the tree parsing, could
we move this recursion out of this function (and then into parse() directly)?
(and actually if change parse to recurse over the tree like my comment above,
both cases would advance the same way through the recursion, just with different
args).

[kuan, 2014/04/18 00:19:03]

Done.  i'm not sure if i code it the way u want regarding "both cases would
advance the same way through the recursion, just with different args".

[cjhopman, 2014/04/18 01:17:01]

See the new comment in parse() for what I meant by that.

+        return newItem;
+    }
+
+    private Type getType(Element e) {
+        String type = e.getAttribute("ITEMTYPE");
+        Set<Map.Entry<Type, String>> typeUrls = mTypeUrls.entrySet();
+        Iterator<Map.Entry<Type, String>> iter = typeUrls.iterator();

[cjhopman, 2014/04/17 17:35:26]

I think you can do:

for (Map.Entry<Type, String> typeUrl : mTypeUrls.entrySet()) {
  if (typeUrl...) return ...;
}

[kuan, 2014/04/18 00:19:03]

Done.  since it's now a HashMap of <String, Type>, i just need to use
containsKey() and get().

+        while (iter.hasNext()) {
+            Map.Entry<Type, String> typeUrl = iter.next();
+            if (typeUrl.getValue().equalsIgnoreCase(type)) return typeUrl.getKey();
+        }
+        return Type.UNSUPPORTED;
+    }
+
+    // Extract the value of the "itemprop" attribute in |e|.
+    // @param currItem ThingItem-extended item for the current Schema.org type being parsed.
+    // @param embeddedItem ThingItem-extended item for the Schema.org type created for |e|, i.e. |e|    // had specified a Schema.org type.
+    private void extractProperty(Element e, ThingItem currItem, ThingItem embeddedItem) {

[cjhopman, 2014/04/17 17:35:26]

This function does a lot (and most of what it does isn't reflected in the name).
It gets the itemprop and then adds the embedded item to current item or gets the
element's property value and then adds that property to the current item.

This would be clearer as two functions:
getItemprop(Element)
getPropertyValue(Element)

and then handle the putItem/putString separately elsewhere.

If you keep this function close to what it currently is, the name should at
least indicate that it will add the extracted property to currItem.

[kuan, 2014/04/18 00:19:03]

Done.

+        // "itemprop" attribute is case-sensitive.
+        String name = e.getAttribute("ITEMPROP");
+        if (name == null || name.isEmpty()) return;
+        if (embeddedItem != null) {  // This "itemprop" attribute is an embedded item.
+            currItem.putItemValue(name, embeddedItem);
+        } else {  // Extract value from the tag.
+            String value = null;
+            if (e.hasTagName("A")) {
+                value = AnchorElement.as(e).getHref();
+            } else if (e.hasTagName("IMG")) {
+                value = ImageElement.as(e).getSrc();
+            } else if (e.hasTagName("META")) {
+                value = MetaElement.as(e).getContent();
+            } else if (e.hasTagName("TIME")) {
+                value = e.getAttribute("datetime");
+            }
+            if (value == null || value.isEmpty()) value = e.getInnerText();
+            currItem.putStringValue(name, value);
+        }
+    }
+
+    // Returns the first item that has the requested property value.
+    private String findStringProperty(String name) {
+        if (mItemScopes.isEmpty()) return null;
+        for (int i = 0; i < mItemScopes.size(); i++) {
+            String value = mItemScopes.get(i).getStringProperty(name);
+            if (!value.isEmpty()) return value;
+        }
+        return "";
+    }
+
+    private static class ImageItem extends ThingItem {
+        private static final String[] mStringPropertyNames = {
+            NAME_PROP,
+            URL_PROP,
+            DESCRIPTION_PROP,
+            IMAGE_PROP,
+            HEADLINE_PROP,
+            PUBLISHER_PROP,
+            COPYRIGHT_HOLDER_PROP,
+            COPYRIGHT_YEAR_PROP,
+            CONTENT_URL_PROP,
+            ENCODING_FORMAT_PROP,
+            CAPTION_PROP,
+            REPRESENTATIVE_PROP,
+            WIDTH_PROP,
+            HEIGHT_PROP,
+        };
+
+        private static final String[] mItemPropertyNames = {
+            PUBLISHER_PROP,
+            COPYRIGHT_HOLDER_PROP,
+        };
+
+        protected ImageItem(Element elem) {
+            super(Type.IMAGE, elem, mStringPropertyNames, mItemPropertyNames);
+        }
+
+        @Override
+        protected MarkupParser.Image getImage() {
+            MarkupParser.Image image = new MarkupParser.Image();
+            String url = getStringProperty(CONTENT_URL_PROP);
+            image.image = !url.isEmpty() ? url : getStringProperty(NAME_PROP);
+            image.url = image.image;
+            image.type = getStringProperty(ENCODING_FORMAT_PROP);
+            image.caption = getStringProperty(CAPTION_PROP);
+            try {
+                image.width = Integer.parseInt(getStringProperty(WIDTH_PROP), 10);
+            } catch (Exception e) {
+            }
+            try {
+                image.height = Integer.parseInt(getStringProperty(HEIGHT_PROP), 10);
+            } catch (Exception e) {
+            }
+            return image;
+        }
+    }
+
+    private static class ArticleItem extends ThingItem {
+        private static final String[] mStringPropertyNames = {
+            NAME_PROP,
+            URL_PROP,
+            DESCRIPTION_PROP,
+            IMAGE_PROP,
+            HEADLINE_PROP,
+            PUBLISHER_PROP,
+            COPYRIGHT_HOLDER_PROP,
+            COPYRIGHT_YEAR_PROP,
+            DATE_MODIFIED_PROP,
+            DATE_PUBLISHED_PROP,
+            AUTHOR_PROP,
+            SECTION_PROP,
+        };
+
+        private static final String[] mItemPropertyNames = {
+            PUBLISHER_PROP,
+            COPYRIGHT_HOLDER_PROP,
+            AUTHOR_PROP,
+        };
+
+        protected ArticleItem(Element elem) {
+            super(Type.ARTICLE, elem, mStringPropertyNames, mItemPropertyNames);
+        }
+
+        @Override
+        protected MarkupParser.Article getArticle() {
+            MarkupParser.Article article = new MarkupParser.Article();
+            article.publishedTime = getStringProperty(DATE_PUBLISHED_PROP);
+            article.modifiedTime = getStringProperty(DATE_MODIFIED_PROP);
+            article.section = getStringProperty(SECTION_PROP);
+            String author = getStringProperty(AUTHOR_PROP);
+            article.authors = author.isEmpty() ? new String[0] : new String[] { author };
+            return article;
+        }
+    }
+
+    private static class PersonItem extends ThingItem {
+        private static final String[] mStringPropertyNames = {
+            NAME_PROP,
+            URL_PROP,
+            DESCRIPTION_PROP,
+            IMAGE_PROP,
+            FAMILY_NAME_PROP,
+            GIVEN_NAME_PROP,
+        };
+
+        protected PersonItem(Element elem) {
+            super(Type.PERSON, elem, mStringPropertyNames, new String[0]);
+        }
+
+        // Returns either the value of NAME_PROP, or concatenated values of GIVEN_NAME_PROP and
+        // FAILY_NAME_PROP delimited by a whitespace.
+        @Override
+        protected String toStringProperty() {
+            String fullname = getStringProperty(NAME_PROP);
+            if (fullname.isEmpty()) {
+                fullname = concat(getStringProperty(GIVEN_NAME_PROP),
+                                  getStringProperty(FAMILY_NAME_PROP));
+            }
+            return fullname;
+        }
+    }
+
+    private static class OrganizationItem extends ThingItem {
+        private static final String[] mStringPropertyNames = {
+            NAME_PROP,
+            URL_PROP,
+            DESCRIPTION_PROP,
+            IMAGE_PROP,
+            LEGAL_NAME_PROP,
+        };
+
+        protected OrganizationItem(Element elem) {
+            super(Type.ORGANIZATION, elem, mStringPropertyNames, new String[0]);
+        }
+
+        // Returns either the value of NAME_PROP or LEGAL_NAME_PROP.
+        @Override
+        protected String toStringProperty() {
+            String name = getStringProperty(NAME_PROP);
+            if (name.isEmpty()) name = getStringProperty(LEGAL_NAME_PROP);
+            return name;
+        }
+    }
+
+    private static String concat(String first, String second) {
+        String concat = first;
+        if (!concat.isEmpty() && !second.isEmpty()) concat += " ";
+        concat += second;
+        return concat;
+    }
+}