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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Building Taxonomies with Triplet Queries</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Donatella Firmani</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Sainyam Galhotra</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Barna Saha</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Divesh Srivastava</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>T Chief Data Ofice</string-name>
        </contrib>
      </contrib-group>
      <pub-date>
        <year>1800</year>
      </pub-date>
      <abstract>
        <p>The organization of records referring to diferent entities into a taxonomy is crucial for capturing their relationships. Nevertheless, the automatic identification of such relationships often faces inaccuracies due to noise and heterogeneity of records across various sources. Simultaneously, manual maintenance of these relationships proves impractical and lacks scalability. This study addresses these challenges by adopting a weak supervision strategy, in the form of an oracle, to solve a novel Hierarchical Entity Resolution task. Within our framework, records are organized into a tree-like structure that encompasses records at the bottom level and encapsulates entities and categories at the higher levels. To make the most efective use of supervision, we employ a triplet comparison oracle, which takes three records as input and output the most similar pair(s). Finally, we introduce HierER, a querying strategy utilizing record pair similarities to minimize the number of oracle queries while simultaneously maximizing the identification of the hierarchical structure. Theoretical and empirical analyses demonstrate the efectiveness and eficiency of HierER with noisy datasets with millions of records.</p>
      </abstract>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        In many applications, records are represented in diverse formats like images, unstructured
and structured text and these records need to be organized to capture complex relationships.
Assigning records to taxonomies is useful for diverse applications like recommendation [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ],
categorization [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], and search [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. For example, e-commerce websites like Amazon organize
products in the form of a taxonomy to enable better search and recommendations. Animal and
plant species along with their textual descriptions can be arranged in hierarchies of varying
depth, average degree and shape, called pylogenetic trees. In Figure 1a we show an example
hierarchy for arranging a collection of records describing birds. Example records are  and ,
describing respectively the little bunting (Emberiza pusilla) and the yellow-breasted bunting
(Emberiza aureola). Example categories in the hierarchy is 1. Note that categories are not
required to have a descriptive name: in this example the category 1 is simply defined as the
set comprising the little bunting () and the yellow-breasted bunting ().
      </p>
      <p>Two main types of relationships arise naturally in a hierarchy:
• is-A (in orange) connecting record-nodes such as  to category-nodes such as 1;
• category-supercategory (in black) connecting pairs of category-nodes such as 1 to 2;</p>
      <p>Pinicola
EmberizaEnucleator
melanocepha</p>
      <p>la</p>
      <p>Emrubsteirciaza Empablelarsizia scEhmobeenricizlaus
u1</p>
      <p>Pinicola</p>
      <p>EmberizaEnucleator
ue1a eb um1elanloacepha
r2 Emrrubs3teirciaza Ermpa4blelarsizia scEhmobeenrircizlau5sEmrubsteirciaza Empablelarsizia scEhmobeenricizlaus
Empubseilrliaza Eamubreeorilza(ab) Empubseilrliaza Eamubreeorilzaa</p>
      <p>Pinic
EmberizaEnucle
melanocepha
la
In order to account for duplicate records, that are, diferent records referring to the same entity
in the real world, we introduce a third type of relationship, that we call co-reference. In Figure 1b,
the co-reference relationship is shown in green. To represent this relationship we introduce
intermediate entity-nodes, such as  and , between record-nodes and category-nodes. In the
ifgure, records 1, 2 and 3 are diferent pictures of little bunting, which is now represented by
, while records 4, 5 both represent a yellow-breasted bunting, that we now call . Both 
and  belong to the 1 category, which can be equivalently defined as a set of entities.</p>
      <p>Starting from records 1, . . . , , our task is to return the complete tree structure, identifying
duplicate records and enriching them with is-A and category-supercategory relationships. We
call this problem as the Hierarchical Entity Resolution (HER) problem. The popular Entity
Resolution (ER) problem corresponds to identification of record-entity relationships only (see
green edges in Figure 1b) and thus our problem represents a natural extension.</p>
      <p>Before our work there are two main roads to the solution of HER.</p>
      <p>
        • Fully automatic construction. To automatically construct categories and identify
their relationships, prior techniques have proposed to leverage co-occurence patterns of
hypernyms [
        <xref ref-type="bibr" rid="ref4 ref5">4, 5</xref>
        ]. However, certain categories may not always be explicitly mentioned in
the records [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ] nor respect the same terminology across diferent sources.
• Fully manual Construction. A domain expert can easily generate a hierarchy that
contains all well-known categories. However, it might be impossible to capture all the
ifne-grain relationships in the data (such as, very specialized category-nodes like 1 and
2 in Example 1) without processing all the records manually, which is not scalable.
Even though the benefits of constructing a hierarchy are widely acknowledged, due to
limitations of fully automatic construction, the majority of category-supercategory relationships
are maintained manually by domain experts. Manual maintenance of such relationships is
labor-intensive as the hierarchy evolves whenever new records are introduced/discontinued.
Our intuition. We aim at using a hybrid weakly supervised approach; that is, an automatic
approach that is guided by domain experts providing answers to targeted queries. While
manually processing all the records might be infeasible, if only three records are considered in
isolation, say 1, 2 and 4, then a user – or even a trained classifier – can easily distinguish that
1 and 2 are closer to each other than either of them is to 3. Even though considering record
triplets in isolation can help uncover the hierarchical structure, it is still unfeasible to compare all
possible triples in million scale datasets. Our framework is capable of automatically prioritizing
records to optimize the number of triplet comparisons and to minimize the query workload. We
refer to the domain expert (or the classifier) using the abstraction of a black-box oracle.
Oraclebased algorithms have been widely popular to study fairness [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ], correlation clustering [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ]
and classification [
        <xref ref-type="bibr" rid="ref10 ref9">9, 10</xref>
        ], identify maximum elements [
        <xref ref-type="bibr" rid="ref11 ref12">11, 12</xref>
        ], top- elements [
        <xref ref-type="bibr" rid="ref13 ref14 ref15">13, 14, 15</xref>
        ],
information retrieval [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ], skyline computation [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ], and so on. Our oracle can answer to:
• triplet queries: “which pair of records among ,  and  are most similar?”
• co-reference queries: “do records  and  refer to the same entity?”;
These queries can reveal the local hierarchical structure and can be answered without requiring
(i) the context of all the identified categories in the constructed hierarchy, nor (ii) the knowledge
of other records in the dataset. Recent advancements of deep-learning based classifiers for
ER [
        <xref ref-type="bibr" rid="ref18 ref19 ref20 ref21">18, 19, 20, 21</xref>
        ] are also alternative implementation of our oracle.
      </p>
      <p>
        Related works and oracle-based methods. The closest task to our problem is ER,
featuring a variety of oracle-based methods [
        <xref ref-type="bibr" rid="ref22 ref23 ref24">22, 23, 24</xref>
        ]. However ER techniques typically ignore
category information.Another related task is Hierarchical Clustering. This has been studied
in a variety of application domains including the construction of phylogenetic trees [
        <xref ref-type="bibr" rid="ref25 ref26">25, 26</xref>
        ]
and taxonomies [
        <xref ref-type="bibr" rid="ref27 ref28">27, 28</xref>
        ]. The work in [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ] describes an oracle-based method. In
Hierarchical Clustering, records refer to diferent entities, and thus clustering methods ignore entity
resolution. Moreover, these techniques build almost binary hierarchies, where every node
has approximately two children. Thus, neither ER nor Hierarchical Clustering techniques can
by itself solve our HER problem efectively. Even pipelining the two processes turns out to
achieve a sub-optimal query workload. Let  be the number of records. Running a hierarchical
clustering technique first and then post-processing the bottom level in order to detect entities
can require (2) oracle queries for non-binary hierarchies in the worst case [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ], before even
identifying the entities. Running an oracle-based ER technique first and post-processing entities
after that to detect categories can be eficient in case of large entities but can require (2)
queries to identify small entity clusters [
        <xref ref-type="bibr" rid="ref23">23</xref>
        ], before even starting to process categories.
Contributions and Outline. We show that previous methods can be significantly
outperformed by our approach, thus alleviating the manual workload required for construction and
maintenance of taxonomies over very large databases. Section 2 contains a high-level overview
of our approach, and in particular of the HierER algorithm. Detailed description of the
algorithm and theoretical analysis can be found in [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ]. Main experimental results of [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ] are
reported in Section 3. Finally, Section 4 contain our concluding remarks.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Overview</title>
      <p>Let  = {1, 2, . . . , } be a collection of  records. We use the notion of laminar family of
sets to define the ground truth hierarchy * more formally. A family of sets * is laminar if
∀1, 2 ∈ * , either 1 ∩ 2 =  or 1 ⊆ 2 or 2 ⊆ 1. The hierarchy * corresponds to
a laminar family of labelled sets * such that each set in * is labelled with one of the three labels:
record (r), entity (e) or category (t). Each labelled set is denoted as ⟨label : ⟩
where  ⊆  . According to this notation, ⟨r : {}⟩ ∈ * , ∀ ∈  and ⟨t :  ⟩ ∈ * . This
hierarchy has an additional constraint that a set labelled ‘entity’ cannot have a proper superset
of label ‘entity’ or ‘record’ and a set labelled ‘category’ cannot have a superset labelled
‘entity’ or ‘record’. Following this definition, there exists a one-to-one mapping between
internal nodes of the hierarchy and the laminar family of sets * where an internal node of the
hierarchy (say ) is equivalent to a set  ∈ * containing all the leaf-level descendants of 
and vice versa. In this formulation, a category node that has a single category node as a child is
redundant and can be ignored. However, an entity can have a single child (record).</p>
      <p>
        A hierarchy has an interesting property that for any three records 1, 2, 3 ∈  , the lca’s
of two pairs of these records are the same and the lca of the third pair is either the same or a
descendant of the other two lca’s [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ]. Without loss of generality, one of the following hold.
      </p>
      <p>lca(2, 3) ≥ lca(1, 2) = lca(1, 3)
where lca(1, 2) &gt; lca(, ) denotes that lca(1, 2) is a descendant of lca(, ). In case
all three lca’s are the same, then 1, 2 and 3 belong to three diferent descendant-branches of
the internal node corresponding to lca(1, 2) = lca(1, 3) = lca(2, 3). A triplet oracle is
a function  :  ×  ×  →  ∪ {} that takes three records as input and outputs the farthest
record (if any). For an input (1, 2, 3), the oracle outputs (1, 2, 3) = 1 if lca(2, 3) &gt;
lca(1, 2) = lca(1, 3) and (1, 2, 3) =  if lca(1, 2) = lca(1, 3) = lca(2, 3).</p>
      <p>Prioritizing triplet oracle queries to maximize the accuracy in the * estimation task after
every query, is the goal of the high-level workflow presented in Figure 2. Note that evaluating
accuracy is non-trivial. A naive way is to compare the fraction of the total Θ( 3) relationships
(i.e., (︀ )︀ triplets and (︀ )︀ equality relationships) that are correctly identified by a given method.</p>
      <p>
        3 2
However, such an approach can be infeasible even in medium-sized datasets. Therefore, we
extend the popular metric of comparing F-score of diferent ER techniques to our hierarchical
setting. In ER, F-score is computed over two types of pairwise relationships: intra-cluster and
inter-cluster. Following these ideas, we consider co-reference relationships as intra-cluster and
enumerate the diferent types of inter-entity relationships between record pairs. We define
the notion of t-ancestor relationship to capture the distance between record pairs and then
use it to compute the F-score of the output hierarchy . A pair of records (, ) satisfies a
t-ancestor relationship if their lca is at most t edges away from both  and ’s entity nodes.
0-ancestor relationship is equivalent to an equality (i.e., co-reference) relationship. We map
t-ancestor relationships identified from the output hierarchy  to the ground truth hierarchy
* and then use those to compute precision as the weighted fraction of correctly identified
pairwise relationships among the identified relationships and recall as the weighted fraction of
total relationships that were identified. Weighting mechanisms are discussed in detail in [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ].
F-score is finally computed as the harmonic mean of precision and recall.
      </p>
      <p>Auxiliary modules. In the following, we first describe the auxiliary modules in Figure 2, then
we provide more intuition on the core Oracle strategy module.</p>
      <p>
        • The Blocking module is used to reduce the number of pairs considered for similarity
computation. Blocking is a widely used operation in ER literature [
        <xref ref-type="bibr" rid="ref30">30</xref>
        ] to eficiently
generate a small set of candidate pairs so that similarity values are computed only for this
small set of candidates. Standard blocking (also known as token-based blocking) is one of
the most popular mechanisms that generates a block for each token in the input set of
records [
        <xref ref-type="bibr" rid="ref30">30</xref>
        ]. Similarity values may not be directly interpretable as probability distributions
over the possible oracle responses. For practical purposes, calibration approach in [
        <xref ref-type="bibr" rid="ref23 ref31">23, 31</xref>
        ]
can be used to map values (1, 2) to probability distributions (1, 2) and (1, 2, 3).
similarity values of record pairs probability
calibration
estimated oracle
answers probabilities
set of
records
blocking and
      </p>
      <p>similarity
similarity values of record pairs initialization
candidate
hierarchy</p>
      <p>T/F
inference
inferred
relationships
oracle
strategy
u,v u,v,w
hierarchy
u/v/w/ϕ
equality oracle
triplet oracle</p>
      <p>
        • The Initialization module in our workflow constructs a candidate hierarchy ¯ that can
be used downstream to guide the querying strategies. Construction of ¯ is based solely
on the similarity scores  :  ×  → [
        <xref ref-type="bibr" rid="ref1">0, 1</xref>
        ] and requires no oracle queries. We prove
in [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ] that ¯ has high F-score under low noise of similarity values.
• The Inference module provides tools to infer relationships from previously asked triplet
and equality queries, without asking new oracle queries leading to unnecessary cost. Such
module allows to infer, for instance, which is the farthest record among ,  and  by
looking at the result of previous queries about other triples like (, , ) and (, , ).
      </p>
      <p>We observe that inferring category-subcategory relationships is the major challenge, whereas
co-reference can be easily inferred via transitive closure.1 Consider three records 1, 2, 6
and a query 1 ≡ (1, 2, 6) that returns 6. To interpret 1 mathematically, we define
three variables corresponding to the lca’s of involved record pairs (1, 2), (1, 6) and (2, 6).
Using these variables, 1 can be represented as lca(1, 2) &gt; lca(1, 6) = lca(2, 6).
This inequality characterizes a relation between the lca of record pairs (1, 2), (1, 6) and
(2, 6). Each query can be written in the form of such inequality constraints over at most
︀( 2)︀ lca variables. Consider another query 2 ≡ (1, 6, 11) = 11, meaning lca(1, 6) &gt;
(1, 11) = lca(6, 11). Using the inequalities of 1 and 2, we can infer that lca(1, 2) &gt;
lca(1, 6) &gt; lca(1, 11).</p>
      <p>
        Oracle strategy. This module prioritizes oracle queries by leveraging (i) the candidate hierarchy
from the initialization step to give higher priority to queries that yield higher F-score increment
and (ii) the inference engine to identify inferable relationships for free. The algorithm HierER
described in [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ] can be thought of as an oracle strategy that leverage the initialization and
inference methods and focus on the following principles to maximize progressive F-score.
• Internal node discovery. Prioritize queries that enable the discovery of new internal nodes.
      </p>
      <p>
        Indeed, identifying the tree structure, specifically the internal nodes between the root
node and the leaf nodes corresponding to the processed records is important to provide
optimal progressive behavior.
• Large entities. Give high priority to queries enabling the discovery of new children of
high-degree entity nodes. This principle has also been used in ER literature [
        <xref ref-type="bibr" rid="ref22 ref23">23, 22</xref>
        ] since
asking queries in non-increasing order of entity sizes provides the maximum gain in
1E.g., if we know that 1 refers to the same entity as 2, and 2 refers to the same entity as 3, then we can infer
that 1 refers to the same entity as 3 without asking the corresponding oracle query.
      </p>
      <p>n
1039
100K
16.5K
30K
30K
3M</p>
      <p>progressive recall.
• Connectivity. Prioritize queries that grow the hierarchy in a connected fashion. Indeed,
ensuring that the processed records at any given time form a single connected hierarchy
(rather than growing multiple disjoint hierarchies in parallel) allows for the inference of
more relationships with the same number of queries.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Experiments</title>
      <p>
        We now compare HierER and baselines on real-world datasets and answer the following
questions. Q1: What is the end-to-end quality vs query complexity trade of for HierER? Q2:
Is HierER sensitive to noise in the dataset? Q3: Is HierER scalable to large-scale datasets?
Set-up. Figure 3 reports the six real-world datasets in our experiments, consisting of hierarchies
of varying depth, average degree and shape, and comprising either textual (records) or visual
description (images) of entities. Phylogenetic contains scientific names of bird and insect
species along with textual descriptions collected from Wikipedia. The hierarchy corresponds to
the phylogenetic tree obtained from [
        <xref ref-type="bibr" rid="ref32">32</xref>
        ]. Figure 1a in Section 1 shows the shape of such
hierarchy. DMOZ [33] is an open-content directory of web pages along with a hierarchy that organizes
these webpages according to their categories like art, science, mathematics, etc. Cars comprises
images of diferent models of cars. For Cars we generate textual descriptions using Google’s
vision API [34] and hierarchy is constructed based on their make and model. Camera [35] is a
collection of specifications of cameras collected from over 25 retail companies and the hierarchy
corresponds to the brand-model categorization. Amazon [36] contains descriptions of products
and the amazon catalog ontology. Geography [37] contains names of cities across the world
with categories corresponding to their state, country and continent.
      </p>
      <p>
        Due to low-training data requirements for random forests as compared to deep-learning
based techniques [
        <xref ref-type="bibr" rid="ref20">20</xref>
        ], we used a random forest classifier trained with active learning for cars,
geography and camera datasets as an oracle. Such model achieved more than 0.95 F-score for
all three datasets. For other datasets we consider a simulated oracle model (i.e., using ground
truth hierarchy to generate responses) to control the noise level. For more implementation
details such as similarity calculation and triplet probability we refer the reader to [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ].
      </p>
      <p>
        We consider the following pipelined baseline strategies that perform hierarchical clustering
and entity resolution separately as a two-step procedure. (i) Average Linkage (denoted by
AverageLink) is an Agglomerative clustering technique. We used the sklearn package [38] to
construct the hierarchy and then run triplet queries bottom up to merge neighboring internal
nodes. (ii) HiExpan denotes the automated taxonomy construction technique from [
        <xref ref-type="bibr" rid="ref28">28</xref>
        ] that uses
the initial seed hierarchy to generate other internal nodes assuming access to all internal nodes
2M#querie4sM
(b) dmoz
6M
(a)
1 HiExpan
0.8
roe0.6
c
-s0.4
F
0.2
0
Ideal
      </p>
      <p>Hybrid</p>
      <p>HiExpan
(c)
4K
32ireKK
s
e
u
q
#
1K
0.2#Mqueries</p>
      <p>0.4M 0.6M
(c) amazon
20M</p>
      <p>#querie4s0M
(d) geography</p>
      <p>60M
HierER</p>
      <p>Theory
1
0.8
roe0.6
c
-s0.4
F
0.2
0
InsSort
1
0.8
roe0.6
c
-s0.4
F
0.2
0</p>
      <p>5K
#queries
(a) phylogenetic</p>
      <p>10K</p>
      <p>AverageLink
20K
#queries 40K
(a) cars
(b)</p>
      <p>20K
#queries
(b) camera
40K
0 2 3 4 10</p>
      <p>
        a
(a) Processing error
0 5Perce10ntage15 20
(b) Data error
in the hierachy. We added the internal nodes to run this algorithm. (iii) InsSort considers the
extension of the insertion sort algorithm [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ] for non-binary hierarchies to generate a hierarchy,
followed by Hybrid [
        <xref ref-type="bibr" rid="ref23">23</xref>
        ] to identify equality relationships. (iv) The pipeline that performs ER
followed by hierarchical clustering has almost zero F-score at the end of ER phase when the
datasets contain singleton entities and therefore sufer from poor progressiveness. Instead, we
consider Hybrid as an adaptation of the state-of-the-art entity resolution strategy [
        <xref ref-type="bibr" rid="ref23">23</xref>
        ].
Q1: Result Quality. In order to answer to our first question, we compare the quality of
techniques by measuring the progressive F-score. The F-score value after every query is
computed by mapping the relationships in the constructed hierarchy to those in the the ground
truth hierarchy. Figures 4a and Figures 4b compare the F-score of HierER with other baselines
on multiple datasets. Across all datasets, HierER achieves the highest progressive F-score and
is closest to the ideal curve. InsSort and Hybrid achieve poor progressive F-score. These
techniques require more than 5× the queries required by HierER to achieve comparable F-score
across all large scale datasets. AverageLink generates a hierarchical clustering over the records
without any oracle queries. This hierarchy achieves non-zero F-score but the mistakes in the
constructed hierarchy can not be corrected. HiExpan performs better than AverageLink for
most datasets but does not achieve high F-score. It is sensitive to the initial structure provided
as input and does not generalize if it does not contain all levels of the hierarchy. Due to the
presence of noise in datasets, such automated techniques do not achieve high F-score.
      </p>
      <p>
        We observe diferent behaviors across datasets. In phylogenetic dataset, the ideal requires
&lt; 2 queries as majority of the internal nodes have two children and require less than 2 queries
to be inserted. For each leaf level record, HierER requires (log ) queries to identify its
location in the processed hierarchy [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ], performing better than InsSort but requiring much
more queries than the ideal strategy. This is due to high noise in similarity values, with
more than 85% of the records sufering from data error in this dataset. Among other datasets,
including those with internal nodes having much higher average degree, HierER achieves
near-optimal progressive F-score and performs much better than all other baselines.
      </p>
      <p>
        The experiments in Figure 4 assumes that the oracle answers all queries correctly. For
experiments with independent triplet error we refer the reader to [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ]. To develop robust
methods, we leverage the random graph toolkit [
        <xref ref-type="bibr" rid="ref24">24</xref>
        ] for each oracle query.
      </p>
      <p>
        Q2: Noise sensitivity. To validate the efect of noise, Figure 4c considers synthetic
similarities in the Phylogenetic dataset and compares the query complexity with the theoretically
proven bounds in [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ], where we establish that HierER requires ( log ) triplet comparisons,
assuming reasonable data error. Figure 4c (left) simulates processing error, where each pairwise
similarity ((, )) is sampled independently according to a normal distribution with mean  (,)
and variance  2 =  2 ( denotes the diference in expected similarity for pairs connected
at diferent depths). The query complexity of HierER is the same as that of ideal (roughly
2) for  &lt; 3. For higher noise, the query complexity increases but it plateaus at ( log ).
Figure 4c (right) simulates data error, where a random sample of the nodes is erroneous such
that all pairwise similarities containing these records are erroneous. In this case, the query
complexity of the technique is directly proportional to the error.
      </p>
      <p>Q3: Scalability. Figure 5 compares the running time of HierER to reach 0.90 F-score with
respect to other baselines. HierER has significantly lower running time for all the datasets due
to the linear dependence of running time on the number of queries, finishing in less than 2
minutes on Phylogenetic and in less than 12 hrs on the million-scale Geography dataset.</p>
    </sec>
    <sec id="sec-4">
      <title>4. Conclusions</title>
      <p>In this paper, we have formalized the Hierarchical Entity Resolution problem, introducing
an oracle-based approach. Our algorithm, HierER, presents a novel query ordering strategy
that capitalizes on pairwise record similarities, prioritizing triplet and equality oracle queries.
Theoretical and empirical analysis underscores that HierER is capable of constructing an
accurate hierarchy with a limited query workload across diverse real-world datasets.</p>
    </sec>
    <sec id="sec-5">
      <title>Acknowledgments</title>
      <p>Donatella Firmani has been partially supported by the following research grants: SEED PNR
Project “FLOWER” “Frontiers in Linking records: knOWledge graphs, Explainability and
tempoRal data”, Sapienza Research Project B83C22007180001 “Trustworthy Technologies for
Augmenting Knowledge Graphs” and HORIZON Research and Innovation Action 101135576 INTEND
“Intent-based data operation in the computing continuum”.
[33] Dmoz https://dmoz-odp.org/, 2018.
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