O C T O B E R 1 1 - 1 4 , 2 0 1 6 • B O S T O N , M A

Working with deeply nested documents in Apache Solr
Anshum Gupta, Alisa Zhila
IBM Watson

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Anshum Gupta
• Apache Lucene/Solr committer and PMC member
• Search guy @ IBM Watson.
• Interested in search and related stuff.
• Apache Lucene since 2006 and Solr since 2010.

4
Alisa Zhila
• Apache Lucene/Solr supporter :)
• Natural Language Processing technologies @ IBM Watson
• Interested in search and related stuff

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Agenda
• Hierarchical Data/Nested Documents
• Indexing Nested Documents
• Querying Nested Documents
• Faceting on Nested Documents

Hierarchical Documents

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• Social media comments, Email threads,
Annotated data - AI
• Relationship between documents
• Possibility to flatten
Need for nested data
EXAMPLE: Blog Post with Comments
Peter Navarro outlines the Trump economic plan
Tyler Cowen, September 27, 2016 at 3:07am
Trump proposes eliminating America’s $500 billion
trade deficit through a combination of increased
exports and reduced imports.
1 Ray Lopez September 27, 2016 at 3:21 am
I’ll be the first to say this, but the analysis is flawed.
{negative}
2 Brian Donohue September 27, 2016 at 9:20 am
The math checks out. Solid.
{positive}
examples from http://marginalrevolution.com

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• Can not flatten, need to retain context
• Relationship between documents
• Get all 'positive comments' to 'posts about
Trump' -- IMPOSSIBLE!!!
Nested Documents
EXAMPLE: Data Flattening
Title: Peter Navarro outlines the Trump economic plan
Author: Tyler Cowen
Date: September 27, 2016 at 3:07am
Body: Trump proposes eliminating America’s $500 billion
trade deficit through a combination of increased exports and
reduced imports.
Comment_authors: [Ray Lopez, Brian Donohue]
Comment_dates: [September 27, 2016 at 3:21 am,
September 27, 2016 at 9:20 am]
Comment_texts: ["I’ll be the first to say this, but the analysis is
flawed.", "The math checks out. Solid."]
Comment_sentiments: [negative, positive]

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• Can not flatten, need to retain context
• Relationship between documents
• Get all 'positive comments' to 'posts about
Trump' -- POSSIBLE!!! (stay tuned)
Nested Documents
EXAMPLE: Hierarchical Documents
Type: Post
Title: Peter Navarro outlines the Trump economic plan
Author: Tyler Cowen
Date: September 27, 2016 at 3:07am
Body: Trump proposes eliminating America’s $500 billion
trade deficit through a combination of increased exports and
reduced imports.
Type: Comment
Author: Ray Lopez
Date: September 27, 2016 at 3:21 am
Text: I’ll be the first to say this, but the analysis is flawed.
Sentiment: negative
Type: Comment
Author: Brian Donohue
Date: September 27, 2016 at 9:20 am
Text: The math checks out. Solid.
Sentiment: positive

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• Blog Post Data with Comments and Replies
from http://marginalrevolution.com (cured)
• 2 posts, 2-3 comments per post, 0-3 replies
per comment
• Extracted keywords & sentiment data
• 4 levels of "nesting"
• Too big to show on slides
• Data + Scripts + Demo Queries:
• https://github.com/alisa-ipn/solr-
revolution-2016-nested-demo
Running Example

Indexing Nested Documents

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• Nested XML
• JSON Documents
• Add _childDocument_ tags for all children
• Pre-process field names to FQNs
• Lose information, or add that as meta-data during pre-processing
• JSON Document endpoint (6x only) - /update/json/docs
• Field name mappings
• Child Document splitting - Enhanced support coming soon.
Sending Documents to Solr

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solr-6.2.1$ bin/post -c demo-xml ./data/example-data.xml
Sending Documents to Solr: Nested XML
<add>
<doc>
<field name="type">post</field>
<field name="author"> "Alex Tabarrok"</field>
<field name="title">"The Irony of Hillary Clinton’s Data Analytics"</
field>
<field name="body">"Barack Obama’s campaign adopted data but
Hillary Clinton’s campaign has been molded by data from birth."</field>
<field name="id">"12015-24204"</field>
<doc>
<field name="type">comment</field>
<field name="author">"Todd"</field>
<field name="text">"Clinton got out data-ed and out organized in
2008 by Obama. She seems at least to learn over time, and apply the
lessons learned to the real world."</field>
<field name="sentiment">"positive"</field>
<field name="id">"29798-24171"</field>
<doc>
<field name="type">reply</field>
<field name="author">"The Other Jim"</field>
<field name="text">"No, she lost because (1) she is thoroughly
detested person and (2) the DNC decided Obama should therefore
win."</field>
<field name="sentiment">"negative"</field>
<field name="id">"29798-21232"</field>
</doc>
</doc>
</doc>
</add>

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• Add _childDocument_ tags for all children
• Pre-process field names to FQNs
• Lose information, or add that as meta-data during pre-processing
solr-6.2.1$ bin/post -c demo-solr-json ./data/small-example-data-solr.json -format solr
Sending Documents to Solr: JSON Documents
[{ "path": "1.posts",
"id": "28711",
"author": "Alex Tabarrok",
"title": "The Irony of Hillary Clinton’s Data Analytics",
"body": "Barack Obama’s campaign adopted data but Hillary Clinton’s campaign
has been molded by data from birth.",
"_childDocuments_": [
{
"path": "2.posts.comments",
"id": "28711-19237",
"author": "Todd",
"text": "Clinton got out data-ed and out organized in 2008 by Obama. She
seems at least to learn over time, and apply the lessons learned to the real world.",
"sentiment": "positive",
"_childDocuments_": [
{
"path": "3.posts.comments.replies",
"author": "The Other Jim",
"id": "28711-12444",
"sentiment": "negative",
"text": "No, she lost because (1) she is thoroughly detested person and
(2) the DNC decided Obama should therefore win."
}]}]}]

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• JSON Document endpoint (6x only) - /update/json/docs
• Field name mappings
• Child Document splitting - Enhanced support coming soon.
solr-6.2.1$ curl 'http://localhost:8983/solr/gettingstarted/update/json/docs?
split=/|/posts|/posts/comments|/posts/comments/replies&commit=true' --data-
binary @small-example-data.json -H ‘Content-type:application/json'
NOTE: All documents must contain a unique ID.
Sending Documents to Solr: JSON Endpoint

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• Update Request Processors don’t work with nested documents
• Example:
• UUID update processor does not auto-add an id for a child document.
• Workaround:
• Take responsibility at the client layer to handle the computation for nested
documents.
• Change the update processor in Solr to handle nested documents.
Update Processors and Nested Documents

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• The entire block needs reindexing
• Forgot to add a meta-data field that might be useful? Complete reindex
• Store everything in Solr IF
• it’s too expensive to reconstruct the doc from original data source
• No access to data anymore e.g. streaming data
Re-Indexing Your Documents

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• Various ways to index nested documents
• Need to re-index entire block
Nested Document Indexing Summary

Let’s ask some interesting questions

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{
"path":["4.posts.comments.replies.keywords"],
"text":["Trump"]},
{
"path":["3.posts.comments.keywords"],
"text":["Trump"]},
{
"path":["2.posts.keywords"],
"text":["Trump"]},
{
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is funnier."],
"path":["3.posts.comments.replies"]},
{
"text":["Trump proposes eliminating America’s $500 billion trade deficit through a combination of increased exports and reduced imports."],
"path":["1.posts"]},
{
"text":["Hillary was impressive, for sure, and Trump spent time spluttering and floundering, but he was actually able to find his feet and score some points."],
"path":["2.posts.comments"]}
Easy question first
Find all documents that mention Trump
q=text:Trump

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{
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is funnier."],
"path":["3.posts.comments.replies"]},
{
"text":["Hillary was impressive, for sure, and Trump spent time spluttering and floundering, but he was actually able to find his feet and score some points."],
"path":["2.posts.comments"]},
{
"text":["No one goes to Clinton rallies while tens of thousands line up to see Trump, data-mining leads to a fantasy view of the World."],
"path":["2.posts.comments"]}
Returning certain types of documents
Find all comments and replies that mention Trump
q=(path:2.posts.comments OR path:3.posts.comments.replies) AND text:Trump
Recipe:
At the data pre-processing stage, add a field that indicates document type
and also its path in the hierarchy (-- stay tuned):

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{
"path":["3.posts.comments.keywords"],
"sentiment":["positive"],
"text":["Hillary"]},
{
"path":["4.posts.comments.replies.keywords"],
"sentiment":["negative"],
"text":["Hillary"]},
{
"path":["2.posts.keywords"],
"text":["Hillary"]}
Returning similar type from different level
Find all keywords that are Hillary
q=path:*.keywords AND text:Hillary
Recipe:
Use wild-cards in the field that stores the hierarchy path

Cross-Level Querying

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{
"path":["3.posts.comments.keywords"],
"sentiment":["positive"],
"text":["Hillary"]},
{
"path":["4.posts.comments.replies.keywords"],
"sentiment":["negative"],
"text":["Hillary"]},
{
"path":["2.posts.keywords"],
"text":["Hillary"]}
Recap so far...
Find all keywords that are Hillary
q=path:*.keywords AND text:Hillary
We're querying precisely for documents
which we provide a search condition for
Query
Level 3
Result
Level 3
Query
Level 4
Result
Level 4
Query
Level 2
Result
Level 2

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Returning parents by querying children:
Block Join Parent Query
Find all comments whose keywords detected positive sentiment towards Hillary
q={!parent which="path:2.posts.comments"}path:3.posts.comments.keywords AND text:Hillary AND sentiment:positive
Query
Level 3
Result
Level 2
{
"author":["Brian Donohue"],
"text":["Hillary was impressive, for sure, and Trump spent time spluttering and floundering,
but he was actually able to find his feet and score some points."],
"path":["2.posts.comments"]},
{
"author":["Todd"],
"text":["Clinton got out data-ed and out organized in 2008 by Obama. She seems at least to
learn over time, and apply the lessons learned to the real world."],
"path":["2.posts.comments"]}

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{
"sentiment":["negative"],
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is funnier."],
"path":["3.posts.comments.replies"]},
{
"sentiment":["neutral"],
"text":["So then I guess he will also eliminate the current account surplus? What will happen to U.S.
asset values?"],
"path":["3.posts.comments.replies"]},
{
"sentiment":["positive"],
"text":["Agreed why spend time data-mining for a fantasy view of the world , when instead you can see
a fantasy in person?"],
"path":["3.posts.comments.replies"]}
Returning children by querying parents:
Block Join Child Query
Find replies to negative comments
q={!child of="path:2.posts.comments"}path:2.posts.comments AND sentiment:negative&fq=path:3.posts.comments.replies
Query
Level 2
Result
Level 3

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{
"sentiment":["negative"],
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is funnier."],
"path":["3.posts.comments.replies"]},
{
"sentiment":["neutral"],
"text":["So then I guess he will also eliminate the current account surplus? What will happen to U.S.
asset values?"],
"path":["3.posts.comments.replies"]},
{
"sentiment":["positive"],
"text":["Agreed why spend time data-mining for a fantasy view of the world , when instead you can see
a fantasy in person?"],
"path":["3.posts.comments.replies"]}
Returning children by querying parents:
Block Join Child Query
Find replies to negative comments
q={!child of="path:2.posts.comments"}path:2.posts.comments AND sentiment:negative&fq=path:3.posts.comments.replies
Query
Level 2
Result
Level 3
Block Join Child Query + Filtering Query
A bit counterintuitive and non-symmetrical to the BJPQ

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{
"path":["4.posts.comments.replies.keywords"],
"id":"17413-13550",
"text":["Trump"]},
{
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is funnier."],
"path":["3.posts.comments.replies"],
"id":"17413-66188"},
{
"path":["3.posts.comments.keywords"],
"id":"12413-12487",
"text":["Hillary"]},
{
"text":["Agreed why spend time data-mining for a fantasy view of the world , when instead you can see
a fantasy in person?"],
"path":["3.posts.comments.replies"],
"id":"12413-10998"}
Returning all document's descendants
Block Join Child Query
Find all descendants of negative comments
q={!child of="path:2.posts.comments"}path:2.posts.comments AND sentiment:negative
Query
Level 2
Results
Level 3
Results
Level 4

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Returning all document's descendants
Block Join Child Query
Find all descendants of negative comments
q={!child of="path:2.posts.comments"}path:2.posts.comments AND sentiment:negative
Query
Level 2
Results
Level 3
Results
Level 4
{
"path":["4.posts.comments.replies.keywords"],
"id":"17413-13550",
"text":["Trump"]},
{
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is funnier."],
"path":["3.posts.comments.replies"],
"id":"17413-66188"},
{
"path":["3.posts.comments.keywords"],
"id":"12413-12487",
"text":["Hillary"]},
{
"text":["Agreed why spend time data-mining for a fantasy view of the world , when instead you can see
a fantasy in person?"],
"path":["3.posts.comments.replies"],
"id":"12413-10998"}
Issue: no grouping by parent
What if we want to bring the whole sub-structure?

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Find all negative comments and return them with all their descendants
q=path:2.posts.comments AND sentiment:negative&fl=*,[child parentFilter=path:2.*]
Query
Level 2
Result
Level 2
sub-
hierarchy
Returning document with all descendants:
ChildDocTransformer
{
"sentiment":["negative"],
"text":["I’ll be the first to say this, but the analysis is flawed."],
"path":["2.posts.comments"],
"_childDocuments_":[
{
"path":["4.posts.comments.replies.keywords"],
"text":["Trump"]},
{
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is funnier."],
"path":["3.posts.comments.replies"]},
{
"path":["4.posts.comments.replies.keywords"],
"text":["U.S."]},
{
"text":["So then I guess he will also eliminate the current account surplus? What
will happen to U.S. asset values?"],
"path":["3.posts.comments.replies"]}
]
},
...
Issue: the "sub-hierarchy" is flat

• Returns all descendant documents along with the queried document
• flattens the sub-hierarchy
• Workarounds:
• Reconstruct the document using path ("path":["3.posts.comments.replies"])
information in case you want the entire subtree (result post-processing)
• use childFilter in case you want a specific level
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“This transformer returns all descendant documents of each parent document matching your query in
a flat list nested inside the matching parent document." (ChildDocTransformer cwiki)
Returning document with all descendants:
ChildDocTransformer

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Find all negative comments and return them with all replies to them
q=path:2.posts.comments AND sentiment:negative&fl=*,[child parentFilter=path:2.*
childFilter=path:3.posts.comments.replies]
{
"sentiment":["negative"],
"text":["I’ll be the first to say this, but the analysis is flawed."],
"path":["2.posts.comments"],
"_childDocuments_":[
{
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is
funnier."],
"path":["3.posts.comments.replies"]},
{
"text":["So then I guess he will also eliminate the current account surplus? What
will happen to U.S. asset values?"],
"path":["3.posts.comments.replies"]}
]
},
...
Returning document with specific descendants:
ChildDocTransformer + childFilter
Query
Level 2:comments
Result
Level 2:comments
+ Level 3:replies

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Find all negative comments and return them with all their descendants that mention Trump
q=path:2.posts.comments AND sentiment:negative&fl=*,[child parentFilter=path:2.* childFilter=text:Trump]
{
"sentiment":["negative"],
"text":["I’ll be the first to say this, but the analysis is flawed."],
"path":["2.posts.comments"],
"_childDocuments_":[
{
"path":["4.posts.comments.replies.keywords"],
"text":["Trump"]},
{
"text":["LOL. I enjoyed Trump during last night’s stand-up bit, but this is
funnier."],
"path":["3.posts.comments.replies"]}
]
},
...
Returning document with queried descendants:
ChildDocTransformer + childFilter
Query
Level 2:comments
Result
Level 2:comments
+ sub-levels
Issue: cannot use boolean expressions in childFilter query

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Cross-Level Querying Mechanisms:
• Block Join Parent Query
• Block Join Children Query
• ChildDocTransformer
Good points:
• overlapping & complementary features
• good capabilities of querying direct ancestors/descendants
• possible to query on siblings of different type
Drawbacks:
• need for data-preprocessing for better querying flexibility
• limited support of querying over non-directly related branches (overcome with graphs?)
• flattening nested data (additional post-processing is needed for reconstruction)
Nested Document Querying Summary

Faceting on Nested Documents

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• Solr allows faceting on nested documents!
• Two mechanisms for faceting:
• Faceting with JSON Facet API (since Solr 5.3)
• Block Join Faceting (since Solr 5.5)
Faceting on Nested Documents

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q=path:2.posts.comments AND sentiment:positive&
json.facet={
most_liked_authors : {
type: terms,
field: author,
domain: { blockParent : "path:1.posts"}
}}
Faceting on parents by descendants
JSON Facet API: Parent Domain
Count authors of the posts that received positive comments
"most_liked_authors":{
"buckets":[
{
"val":"Alex Tabarrok",
"count":1},
{
"val":"Tyler Cowen",
"count":1}
]
}
Query
Level 2
Facet
Level 1

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Faceting on descendants by ancestors
JSON Facet API: Child Domain
Distribution of keywords that appear in comments and replies by the top-level posts
Query
Level 1
Facet
Descendant
Levels
"top_keywords":{
"buckets":[{
"val":"hillary",
"count":4,
"counts_by_posts":2},
{
"val":"trump",
"count":3,
"counts_by_posts":2},
{
"val":"dnc",
"count":1,
"counts_by_posts":1},
{
"val":"obama",
"count":2,
"counts_by_posts":1},
{
"val":"u.s",
"count":1,
"counts_by_posts":1}
]}

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q=path:1.posts&rows=0&
json.facet={
filter_by_child_type :{
type:query,
q:"path:*comments*keywords",
domain: { blockChildren : "path:1.posts" },
facet:{
top_keywords : {
type: terms,
field: text,
sort: "counts_by_posts desc",
facet: {
counts_by_posts: "unique(_root_)"
}}}}}
Faceting on descendants by ancestors
JSON Facet API: Child Domain
Distribution of keywords that appear in comments and replies by the top-level posts
Query
Level 1
Facet
Descendant
Levels

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Faceting on descendants by top-level ancestor
JSON Facet API: Child Domain
Distribution of keywords that appear in comments and replies by the top-level posts
Query
Level 1
Facet
Descendant
Levels
Issue: only the top-ancestor gets the unique "_root_" field by default
q=path:1.posts&rows=0&
json.facet={
filter_by_child_type :{
type:query,
q:"path:*comments*keywords",
domain: { blockChildren : "path:1.posts" },
facet:{
top_keywords : {
type: terms,
field: text,
sort: "counts_by_posts desc",
facet: {
counts_by_posts: "unique(_root_)"
}}}}}

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q=path:2.posts.comments&rows=0&
json.facet={
filter_by_child_type :{
type:query,
q:"path:*comments*keywords",
domain: { blockChildren : "path:2.posts.comments" },
facet:{
top_keywords : {
type: terms,
field: text,
sort: "counts_by_comments desc",
facet: {
counts_by_comments: "unique(2.posts.comments-id)"
}}}}}
Faceting on descendants by intermediate ancestors
JSON Facet API: Child Domain + unique fields
Distribution of keywords that appear in comments and replies by the comments
Query
Level 2
Facet
Descendant
Levels
At pre-processing, introduce unique fields for each level

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Faceting on descendants by intermediate ancestors
JSON Facet API: Child Domain + unique fields
Distribution of keywords that appear in comments and replies by the comments
Query
Level 2
Facet
Descendant
Levels
"top_keywords":{
"buckets":[{
"val":"Hillary",
"count":4,
"counts_by_comments":3},
{
"val":"Trump",
"count":3,
"counts_by_comments":3},
{
"val":"DNC",
"count":1,
"counts_by_comments":1},
{
"val":"Obama",
"count":2,
"counts_by_comments":1},
{
"val":"U.S.",
"count":1,
"counts_by_comments":1}
]}

Now let's try the same using Block Join Faceting

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• Experimental Feature
• Needs to be turned on explicitly in solrconfig.xml
More info: https://cwiki.apache.org/confluence/display/solr/BlockJoin+Faceting
Block Join Faceting

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bjqfacet?q={!parent which=path:2.posts.comments}
path:*.comments*keywords&rows=0&facet=true&child.facet.field=text
Faceting on descendants by ancestors #2:
Block Join Faceting on Children Domain
Distribution of keywords that appear in comments and replies by the comments
"facet_fields":{
"text":[
"dnc",1,
"hillary",3,
"obama",1,
"trump",3,
"u.s",1
]
}
Query
Level 2
Facet
Descendant
Levels

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bjqfacet?q={!parent which=path:2.posts.comments}
path:*.comments*keywords&rows=0&facet=true&child.facet.field=text
Faceting on descendants by ancestors #2:
Block Join Faceting on Children Domain
Distribution of keywords that appear in comments and replies by the comments
"facet_fields":{
"text":[
"dnc",1,
"hillary",3,
"obama",1,
"trump",3,
"u.s",1
]
}
Query
Level 2
Facet
Descendant
Levels
bjqfacet request handler instead of query

47
Output Comparison
Block Join Facet JSON Facet API
"facet_fields":{
"text":[
"dnc",1,
"hillary",3,
"obama",1,
"trump",3,
"u.s",1
]
}
"top_keywords":{
"buckets":[{
"val":"Hillary",
"count":4,
"counts_by_comments":3},
{
"val":"Trump",
"count":3,
"counts_by_comments":3},
{
"val":"DNC",
"count":1,
"counts_by_comments":1},
{
"val":"Obama",
"count":2,
"counts_by_comments":1},
{
"val":"U.S.",
"count":1,
"counts_by_comments":1}
]}
Distribution of keywords that appear in comments and replies by the comments

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Output Comparison
Block Join Facet JSON Facet API
"facet_fields":{
"text":[
"dnc",1,
"hillary",3,
"obama",1,
"trump",3,
"u.s",1
]
}
"top_keywords":{
"buckets":[{
"val":"Hillary",
"count":4,
"counts_by_comments":3},
{
"val":"Trump",
"count":3,
"counts_by_comments":3},
{
"val":"DNC",
"count":1,
"counts_by_comments":1},
...
Distribution of keywords that appear in comments and replies by the comments
Output is sorted in alphabetical
order. It cannot be changed
facet:{
top_keywords : {
...
sort: "counts_by_comments desc"
}}}

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JSON Facet API:
• Experimental - but more mature
• More developed and established feature
• bulky JSON syntax
• faceting on children by non-top level ancestors requires introducing unique branch
identifiers similar to "_root_" on each level
Block Join Facet:
• Experimental feature
• Lacks controls: sorting, limit...
• traditional query-style syntax
• proper handling of faceting on children by non-top level ancestors
Hierarchical Faceting Summary

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• Returning hierarchical structure
• JSON facet rollups is in the works - SOLR-8998
• Graph querying might replace a lot of functionalities of cross-level querying - No
distributed support right now.
• There’s more but the community would love to have more people involved!
Community Roadmap

Thank you!
Anshum Gupta anshum@apache.org | @anshumgupta
Alisa Zhila alisa.zhila@gmail.com
https://github.com/alisa-ipn/solr-revolution-2016-nested-demo