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An Effective Neural Network Model for Graph-based Dependency Parsing

An Effective Neural Network Model for Graph-based Dependency Parsing
An Effective Neural Network Model for Graph-based Dependency Parsing

An Effective Neural Network Model for Graph-based Dependency Parsing

Wenzhe Pei Tao Ge Baobao Chang?

Key Laboratory of Computational Linguistics,Ministry of Education, School of Electronics Engineering and Computer Science,Peking University,

No.5Yiheyuan Road,Haidian District,Beijing,100871,China Collaborative Innovation Center for Language Ability,Xuzhou,221009,China.

{peiwenzhe,getao,chbb}@https://www.wendangku.net/doc/2f10629436.html,

Abstract

Most existing graph-based parsing models

rely on millions of hand-crafted features,

which limits their generalization ability

and slows down the parsing speed.In this

paper,we propose a general and effective

Neural Network model for graph-based

dependency parsing.Our model can auto-

matically learn high-order feature combi-

nations using only atomic features by ex-

ploiting a novel activation function tanh-

cube.Moreover,we propose a simple yet

effective way to utilize phrase-level infor-

mation that is expensive to use in conven-

tional graph-based parsers.Experiments

on the English Penn Treebank show that

parsers based on our model perform better

than conventional graph-based parsers.

1Introduction

Dependency parsing is essential for computers to understand natural languages,whose performance may have a direct effect on many NLP applica-tion.Due to its importance,dependency parsing, has been studied for tens of years.Among a vari-ety of dependency parsing approaches(McDonald et al.,2005;McDonald and Pereira,2006;Car-reras,2007;Koo and Collins,2010;Zhang and Nivre,2011),graph-based models seem to be one of the most successful solutions to the challenge due to its ability of scoring the parsing decisions on whole-tree basis.Typical graph-based models factor the dependency tree into subgraphs,rang-ing from the smallest edge(?rst-order)to a con-trollable bigger subgraph consisting of more than one single edge(second-order and third order), and score the whole tree by summing scores of the subgraphs.In these models,subgraphs are usually represented as a high-dimensional feature vectors ?Corresponding author which are fed into a linear model to learn the fea-ture weight for scoring the subgraphs.

In spite of their advantages,conventional graph-based models rely heavily on an enormous num-ber of hand-crafted features,which brings about serious problems.First,a mass of features could put the models in the risk of over?tting and slow down the parsing speed,especially in the high-order models where combinational features cap-turing interactions between head,modi?er,sib-lings and(or)grandparent could easily explode the feature space.In addition,feature design re-quires domain expertise,which means useful fea-tures are likely to be neglected due to a lack of domain knowledge.As a matter of fact,these two problems exist in most graph-based models,which have stuck the development of dependency parsing for a few years.

To ease the problem of feature engineering,we propose a general and effective Neural Network model for graph-based dependency parsing in this paper.The main advantages of our model are as follows:

?Instead of using large number of hand-crafted features,our model only uses atomic fea-tures(Chen et al.,2014)such as word uni-grams and POS-tag unigrams.Feature com-binations and high-order features are auto-matically learned with our novel activation function tanh-cube,thus alleviating the heavy burden of feature engineering in conven-tional graph-based models(McDonald et al., 2005;McDonald and Pereira,2006;Koo and Collins,2010).Not only does it avoid the risk of over?tting but also it discovers useful new features that have never been used in conven-tional parsers.

?We propose to exploit phrase-level informa-tion through distributed representation for phrases(phrase embeddings).It not only

en-

Figure1:First-order and Second-order factoriza-tion strategy.Here h stands for head word,m stands for modi?er word and s stands for the sib-ling of m.

ables our model to exploit richer context in-formation that previous work did not consider due to the curse of dimension but also cap-tures inherent correlations between phrases.

?Unlike other neural network based models (Chen et al.,2014;Le and Zuidema,2014) where an additional parser is needed for ei-ther extracting features(Chen et al.,2014)or generating k-best list for reranking(Le and Zuidema,2014),both training and decoding in our model are performed based on our neu-ral network architecture in an effective way.

?Our model does not impose any change to the decoding process of conventional graph-based parsing model.First-order,second-order and higher order models can be easily implemented using our model.

We implement three effective models with in-creasing expressive capabilities.The?rst model is a simple?rst-order model that uses only atomic features and does not use any combinational fea-tures.Despite its simpleness,it outperforms conventional?rst-order model(McDonald et al., 2005)and has a faster parsing speed.To fur-ther strengthen our parsing model,we incorpo-rate phrase embeddings into the model,which signi?cantly improves the parsing accuracy.Fi-nally,we extend our?rst-order model to a second-order model that exploits interactions between two adjacent dependency edges as in McDonald and Pereira(2006)thus further improves the model performance.

We evaluate our models on the English Penn Treebank.Experiment results show that both our ?rst-order and second-order models outperform the corresponding conventional models.2Neural Network Model

A dependency tree is a rooted,directed tree span-ning the whole sentence.Given a sentence x, graph-based models formulates the parsing pro-cess as a searching problem:

y?(x)=arg max

?y∈Y(x)

Score(x,?y(x);θ)(1)

where y?(x)is tree with highest score,Y(x)is the set of all trees compatible with x,θare model parameters and Score(x,?y(x);θ)represents how likely that a particular tree?y(x)is the correct anal-ysis for x.However,the size of Y(x)is expo-nential large,which makes it impractical to solve equation(1)directly.Previous work(McDonald et al.,2005;McDonald and Pereira,2006;Koo and Collins,2010)assumes that the score of?y(x)fac-tors through the scores of subgraphs c of?y(x)so that ef?cient algorithms can be designed for de-coding:

Score(x,?y(x);θ)=

c∈?y(x)

ScoreF(x,c;θ)(2)

Figure1gives two examples of commonly used factorization strategy proposed by Mcdonald et.al (2005)and Mcdonald and Pereira(2006).The simplest subgraph uses a?rst-order factorization (McDonald et al.,2005)which decomposes a de-pendency tree into single dependency arcs(Fig-ure1(a)).Based on the?rst-order model,second-order factorization(McDonald and Pereira,2006) (Figure1(b))brings sibling information into de-coding.Speci?cally,a sibling part consists of a triple of indices(h,m,s)where(h,m)and(h,s) are dependencies and s and m are successive mod-i?ers to the same side of h.

The most common choice for ScoreF(x,c;θ), which is the score function for subgraph c in the tree,is a simple linear function:

ScoreF(x,c;θ)=w·f(x,c)(3) where f(x,c)is the feature representation of sub-graph c and w is the corresponding weight vector. However,the effectiveness of this function relies heavily on the design of feature vector f(x,c).In previous work(McDonald et al.,2005;McDonald and Pereira,2006),millions of hand-crafted fea-tures were used to capture context and structure information in the subgraph which not only lim-its the model’s ability to generalize well but only slows down the parsing speed.

Figure 2:Architecture of the Neural Network In our work,we propose a neural network model for scoring subgraph c in the tree:

ScoreF (x,c ;θ)=NN (x,c )

(4)

where NN is our scoring function based on neu-ral network (Figure 2).As we will show in the fol-lowing sections,it alleviates the heavy burden of feature engineering in conventional graph-based models and achieves better performance by auto-matically learning useful information in the data.The effectiveness of our neural network de-pends on ?ve key components:Feature Em-beddings ,Phrase Embeddings ,Direction-speci?c

transformation ,Learning Feature

Combinations and

Max-Margin Training .2.1Feature Embeddings

As shown in Figure 2,part of the input to the neu-ral network is feature representation of the sub-graph.Instead of using millions of features as in conventional models,we only use use atomic fea-tures (Chen et al.,2014)such as word unigrams and POS-tag unigrams,which are less likely to be sparse.The detailed atomic features we use will be described in Section 3.Unlike conventional models,the atomic features in our model are trans-formed into their corresponding distributed repre-sentations (feature embeddings).

The idea of distributed representation for sym-bolic data is one of the most important reasons why neural network works in NLP tasks.It is shown that similar features will have similar em-beddings which capture the syntactic and seman-tic information behind features (Bengio et al.,

Figure 3:Illustration for phrase embeddings.h ,m and x 0to x 6are words in the sentence.

2003;Collobert et al.,2011;Schwenk et al.,2012;Mikolov et al.,2013;Socher et al.,2013;Pei et al.,2014).

Formally,we have a feature dictionary D of size |D |.Each feature f ∈D is represented as a real-valued vector (feature embedding)Embed (f )∈R d where d is the dimensionality of the vector space.All feature embeddings stacking together forms the embedding matrix M ∈R d ×|D |.The embedding matrix M is initialized randomly and trained by our model (Section 2.6).2.2

Phrase Embeddings

Context information of word pairs 1such as the de-pendency pair (h,m )has been widely believed to be useful in graph-based models (McDonald et al.,2005;McDonald and Pereira,2006).Given a sen-tence x ,the context for h and m includes three context parts:pre?x ,in?x and suf?x ,as illustrated in Figure 3.We call these parts phrases in our work.

Context representation in conventional mod-els are limited:First,phrases cannot be used as features directly because of the data sparseness problem.Therefore,phrases are backed off to low-order representation such as bigrams and tri-grams.For example,Mcdonald et.al (2005)used tri-gram features of in?x between head-modi?er pair (h,m ).Sometimes even tri-grams are expen-sive to use,which is the reason why Mcdonald and Pereira (2006)chose to ignore features over triples of words in their second-order model to prevent from exploding the size of the feature space.Sec-1

A word pair is not limited to the dependency pair (h,m ).It could be any pair with particular relation (e.g.,sibling pair (s,m )in Figure 1).Figure 3only uses (h,m )as an example.

ond,bigrams or tri-grams are lexical features thus cannot capture syntactic and semantic information behind phrases.For instance,“hit the ball”and “kick the football”should have similar represen-tations because they share similar syntactic struc-tures,but lexical tri-grams will fail to capture their similarity.

Unlike previous work,we propose to use distributed representation(phrase embedding)of phrases to capture phrase-level information.We use a simple yet effective way to calculate phrase embeddings from word(POS-tag)embeddings. As shown in Figure3,we average the word em-beddings in pre?x,in?x and suf?x respectively and get three global word-phrase embeddings.For pairs where no pre?x or suf?x exists,the corre-sponding embedding is set to zero.We also get

global POS-phrase

embeddings which are

in the same way as words.These em-

beddings are then concatenated with feature em-

beddings and fed to the following hidden layer.

Phrase embeddings provide panorama represen-

tation of the context,allowing our model to cap-

ture richer context information compared with the

back-off tri-gram representation.Moreover,as

a distributed representation,phrase embeddings

perform generalization over speci?c phrases,thus

better capture the syntactic and semantic informa-

tion than back-off tri-grams.

2.3Direction-speci?c Transformation

In dependency representation of sentence,the

edge direction indicates which one of the words is

the head h and which one is the modi?er m.Un-

like previous work(McDonald et al.,2005;Mc-

Donald and Pereira,2006)that models the edge

direction as feature to be conjoined with other fea-

tures,we model the edge direction with direction-

speci?c transformation.

As shown in Figure2,the parameters in hidden

layer(W d h,b d h)and the output layer(W d o,b d o)are

bound with index d∈{0,1}which indicates the

direction between head and modi?er(0for left arc

and1for right arc).In this way,the model can

learn direction-speci?c parameters and automati-

cally capture the interactions between edge direc-

tion and other features.

2.4Learning Feature Combination

The key to the success of graph-based dependency

parsing is the design of features,especially com-

binational features.Effective as these features are,

as we have said in Section1,they are prone to

over?tting and hard to design.In our work,we

introduce a new activation function that can auto-

matically learn these feature combinations.

As shown in Figure2,we?rst concatenate the

embeddings into a single vector a.Then a is fed

into the next layer which performs linear trans-

formation followed by an element-wise activation

function g:

h=g(W d h a+b d h)(5)

Our new activation function g is de?ned as fol-

lows:

g(l)=tanh(l3+l)(6)

where l is the result of linear transformation and

tanh is the hyperbolic tangent activation function

widely used in neural networks.We call this new

activation function tanh-cube.

As we can see,without the cube term,tanh-cube

would be just the same as the conventional non-

linear transformation in most neural networks.

The cube extension is added to enhance the abil-

ity to capture complex interactions between input

features.Intuitively,the cube term in each hid-

den unit directly models feature combinations in a

multiplicative way:

(w1a1+w2a2+...+w n a n+b)3=

i,j,k

(w i w j w k)a i a j a k+

i,j

b(w i w j)a i a j...

These feature combinations are hand-designed in

conventional graph-based models but our model

learns these combinations automatically and en-

codes them in the model parameters.

Similar ideas were also proposed in previous

works(Socher et al.,2013;Pei et al.,2014;Chen

and Manning,2014).Socher et.al(2013)and

Pei et.al(2014)used a tensor-based activation

function to learn feature combinations.However,

tensor-based transformation is quite slow even

with tensor factorization(Pei et al.,2014).Chen

and Manning(2014)proposed to use cube func-

tion g(l)=l3which inspires our tanh-cube func-

https://www.wendangku.net/doc/2f10629436.html,pared with cube function,tanh-cube has

three advantages:

?The cube function is unbounded,making the

activation output either too small or too big if

the norm of input l is not properly controlled,

especially in deep neural network.On the

contrary,tanh-cube is bounded by the tanh function thus safer to use in deep neural net-work.

?Intuitively,the behavior of cube function re-sembles the“polynomial kernel”in SVM.

In fact,SVM can be seen as a special one-hidden-layer neural network where the ker-nel function that performs non-linear trans-formation is seen as a hidden layer and sup-port vectors as hidden https://www.wendangku.net/doc/2f10629436.html,pared with cube function,tanh-cube combines the power of“kernel function”with the tanh non-linear transformation in neural network.

?Last but not least,as we will show in Section 4,tanh-cube converges faster than the cube

function although the rigorous proof is still open to investigate.

2.5Model Output

After the non-linear transformation of hidden layer,the score of the subgraph c is calculated in the output layer using a simple linear function:

ScoreF(x,c)=W d o h+b d o(7) The output score ScoreF(x,c)∈R|L|is a score vector where|L|is the number of dependency types and each dimension of ScoreF(x,c)is the score for each kind of dependency type of head-modi?er pair(i.e.(h,m)in Figure1).

2.6Max-Margin Training

The parameters of our model areθ=

{W d

h ,b d

h

,W d o,b d o,M}.All parameters are

initialized with uniform distribution within(-0.01, 0.01).

For model training,we use the Max-Margin cri-terion.Given a training instance(x,y),we search for the dependency tree with the highest score computed as equation(1)in Section2.The object of Max-Margin training is that the highest scor-ing tree is the correct one:y?=y and its score will be larger up to a margin to other possible tree ?y∈Y(x):

Score(x,y;θ)≥Score(x,?y;θ)+ (y,?y) The structured margin loss (y,?y)is de?ned as:

(y,?y)=

n

j

κ1{h(y,x j)=h(?y,x j)}

1-order-atomic

h?2.w,h?1.w,h.w,h1.w,h2.w

h?2.p,h?1.p,h.p,h1.p,h2.p

m?2.w,m?1.w,m.w,m1.w,m2.w

m?2.p,m?1.p,m.p,m1.p,m2.p

dis(h,m)

1-order-phrase

+hm pre?x.w,hm in?x.w,hm suf?x.w

+hm pre?x.p,hm in?x.p,hm suf?x.p

2-order-phrase

+s?2.w,s?1.w,s.w,s1.w,s2.w

+s?2.p,s?1.p,s.p,s1.p,s2.p

+sm in?x.w,sm in?x.p

Table1:Features in our three models.w is

short for word and p for POS-tag.h indicates

head and m indicates modi?er.The subscript rep-

resents the relative position to the center word.

dis(h,m)is the distance between head and modi-

?er.hm pre?x,hm in?x and hm suf?x are phrases

for head-modi?er pair(h,m).s indicates the sib-

ling in second-order model.sm in?x is the in?x

phrase between sibling pair(s,m)

where n is the length of sentence x,h(y,x j)is the

head(with type)for the j-th word of x in tree y and

κis a discount parameter.The loss is proportional

to the number of word with an incorrect head and

edge type in the proposed tree.This leads to the

regularized objective function for m training ex-

amples:

J(θ)=

1

m

m

i=1

l i(θ)+

λ

2

||θ

||2

l i(θ)=max

?y∈Y(x i)

(Score(x i,?y;θ)+ (y i,?y))

?Score(x i,y i;θ))(8) We use the diagonal variant of AdaGrad(Duchi et al.,2011)with minibatchs(batch size=20) to minimize the object function.We also apply dropout(Hinton et al.,2012)with0.5rate to the hidden layer.

3Model Implementation

Base on our Neural Network model,we present three model implementations with increasing ex-pressive capabilities in this section.

3.1First-order models

We?rst implement two?rst-order models:1-order-atomic and1-order-phrase.We use the Eisner(2000)algorithm for decoding.The?rst two rows of Table1list the features we use in these two models.

1-order-atomic only uses atomic features as shown in the?rst row of Table1.Speci?cally,the

Models

Dev Test

Speed(sent/s) UAS LAS UAS LAS

First-order MSTParser-1-order92.0190.7791.6090.3920 1-order-atomic-rand92.0090.7191.6290.4155 1-order-atomic92.1990.9492.1992.1955 1-order-phrase-rand92.4791.1992.2591.0526 1-order-phrase92.8291.4892.5991.3726

Second-order MSTParser-2-order92.7091.4892.3091.0614 2-order-phrase-rand93.3992.1092.9991.7910 2-order-phrase93.5792.2993.2992.1310

Third-order(Koo and Collins,2010)93.49N/A93.04N/A N/A Table2:Comparison with conventional graph-based models.

head word and its local neighbor words that are within the distance of2are selected as the head’s word unigram features.The modi?er’s word un-igram features is extracted in the same way.We also use the POS-tags of the corresponding word features and the distance between head and modi-?er as additional atomic features.

We then improved1-order-atomic to1-order-phrase by incorporating additional phrase embed-dings.The three phrase embeddings of head-modi?er pair(h,m):hm pre?x,hm in?x and hm suf?x are calculated as in Section2.2.

3.2Second-order model

Our model can be easily extended to a second-order model using the second-order decoding al-gorithm(Eisner,1996;McDonald and Pereira, 2006).The third row of Table1shows the addi-tional features we use in our second-order model. Sibling node and its local context are used as additional atomic features.We also used the in-?x embedding for the in?x between sibling pair (s,m),which we call sm in?x.It is calculated in the same way as in?x between head-modi?er pair (h,m)(i.e.,hm in?x)in Section2.2except that the word pair is now s and m.For cases where no sibling information is available,the corresponding sibling-related embeddings are set to zero vector. 4Experiments

4.1Experiment Setup

We use the English Penn Treebank(PTB)to eval-uate our model implementations and Yamada and Matsumoto(2003)head rules are used to extract dependency trees.We follow the standard splits of PTB3,using section2-21for training,section22 as development set and23as test set.The Stanford POS Tagger(Toutanova et al.,2003)with ten-way jackkni?ng of the training data is used for assign-ing POS tags(accuracy≈97.2%).

Hyper-parameters of our models are tuned on the development set and their?nal settings are as follows:embedding size d=50,hidden layer (Layer2)size=200,regularization parameterλ= 10?4,discount parameter for margin lossκ=0.3, initial learning rate of AdaGrad alpha=0.1.

4.2Experiment Results

Table2compares our models with several conven-tional graph-based parsers.We use MSTParser2 for conventional?rst-order model(McDonald et al.,2005)and second-order model(McDonald and Pereira,2006).We also include the result of a third-order model of Koo and Collins(2010)for comparison3.For our models,we report the results with and without unsupervised pre-training.Pre-training only trains the word-based feature embed-dings on Gigaword corpus(Graff et al.,2003)us-ing word2vec4and all other parameters are still initialized randomly.In all experiments,we re-port unlabeled attachment scores(UAS)and la-beled attachment scores(LAS)and punctuation5 is excluded in all evaluation metrics.The parsing speeds are measured on a workstation with Intel Xeon3.4GHz CPU and32GB RAM.

As we can see,even with random initialization, 1-order-atomic-rand performs as well as conven-tional?rst-order model and both1-order-phrase-2https://www.wendangku.net/doc/2f10629436.html,/projects/ mstparser

3Note that Koo and Collins(2010)’s third-order model and our models are not strict comparable since their model is an unlabeled model.

4https://https://www.wendangku.net/doc/2f10629436.html,/p/word2vec/

5Following previous work,a token is a punctuation if its POS tag is{“”:,.}

Figure4:Convergence curve for tanh-cube and cube activation function.

rand and2-order-phrase-rand perform better than conventional models in MSTParser.Pre-training further improves the performance of all three models,which is consistent with the conclu-sion of previous work(Pei et al.,2014;Chen and Manning,2014).Moreover,1-order-phrase per-forms better than1-order-atomic,which shows that phrase embeddings do improve the model.2-order-phrase further improves the performance because of the more expressive second-order fac-torization.All three models perform signi?cantly better than their counterparts in MSTParser where millions of features are used and1-order-phrase works surprisingly well that it even beats the con-ventional second-order model.

With regard to parsing speed,1-order-atomic is the fastest while other two models have similar speeds as MSTParser.Further speed up could be achieved by using pre-computing strategy as men-tioned in Chen and Manning(2014).We did not try this strategy since parsing speed is not the main focus of this paper.

Model tanh-cube cube tanh

1-order-atomic92.1991.9791.73 1-order-phrase92.8292.2592.13 2-order-phrase93.5792.9592.91

Table3:Model Performance of different activa-tion functions.

We also investigated the effect of different acti-vation functions.We trained our models with the same con?guration except for the activation func-tion.Table3lists the UAS of three models on de-velopment set.

Feature Type Instance Neighboors

Words

(word2vec)

in

the,of,and,

for,from

his

himself,her,he,

him,father

which

its,essentially,

similar,that,also

Words

(Our model)

in

on,at,behind,

among,during

his

her,my,their,

its,he

which

where,who,whom,

whose,though

POS-tags

NN

NNPS,NNS,EX,

NNP,POS

JJ

JJR,JJS,PDT,

RBR,RBS

Table4:Examples of similar words and POS-tags according to feature embeddings.

As we can see,tanh-cube function outperforms cube function because of advantages we men-tioned in Section2.4.Moreover,both tanh-cube function and cube function performs better than tanh function.The reason is that the cube term can capture more interactions between input features. We also plot the UAS of2-order-phrase dur-ing each iteration of training.As shown in Figure 4,tanh-cube function converges faster than cube function.

4.3Qualitative Analysis

In order to see why our models work,we made qualitative analysis on different aspects of our model.

Ability of Feature Abstraction

Feature embeddings give our model the ability of feature abstraction.They capture the inherent cor-relations between features so that syntactic similar features will have similar

representations,which makes our model generalizes well on unseen data. Table4shows the effect of different feature embeddings which are obtained from2-order-phrase after training.For each kind of feature type,we list several features as well as top5fea-tures that are nearest(measured by Euclidean dis-tance)to the corresponding feature according to their embeddings.

We?rst analysis the effect of word embeddings after training.For comparison,we also list the initial word embeddings in word2vec.As we can see,in word2vec word embeddings,words that are similar to in and which tends to be those

Phrase Neighboor

On a Saturday morning On Monday night football On Sunday

On Saturday

On Tuesday afternoon

On recent Saturday morning

most of it of it

of it all

some of it also most of these are only some of

big investment bank great investment bank bank investment

entire equity investment another cash equity investor real estate lending division

Table5:Examples of similar phrases according to phrase embeddings.

co-occuring with them and for word his,similar words are morphologies of he.On the contrary, similar words measured by our embeddings have similar syntactic functions.This is helpful for de-pendency parsing since parsing models care more about the syntactic functions of words rather than their collocations or morphologies.

POS-tag embeddings also show similar behav-ior with word embeddings.As shown in Table4, our model captures similarities between POS-tags even though their embeddings are initialized ran-domly.

We also investigated the effect of phrase embed-dings in the same way as feature embeddings.Ta-ble5lists the examples of similar phrases.Our phrase embeddings work pretty well given that only a simple averaging strategy is used.Phrases that are close to each other tend to share simi-lar syntactic and semantic information.By using phrase embeddings,our model sees panorama of the context rather than limited word tri-grams and thus captures richer context information,which is the reason why phrase embeddings signi?cantly improve the performance.

Ability of Feature Learning

Finally,we try to unveil the mysterious hidden layer and investigate what features it learns.For each hidden unit of2-order-phrase,we get its connections with embeddings(i.e.,W d h in Figure 2)and pick the connections whose weights have absolute value>0.1.We sampled several hidden units and invenstigated which features their highly weighted connections belong to:

?Hidden1:h.w,m.w,h?1.w,m1.w

?Hidden2:h.p,m.p,s.p

?Hidden3:hm in?x.p,hm in?x.w,hm pre?x.w

?Hidden4:hm in?x.w,hm pre?x.w,sm in?x.w

?Hidden5:hm in?x.p,hm in?x.w,hm suf?x.w

The samples above give qualitative results of what features the hidden layer learns:

?Hidden unit1and2show that atomic features of head,modi?er,sibling and their local con-text words are useful in our model,which is consistent with our expectations since these features are also very important features in conventional graph-based models(McDon-ald and Pereira,2006).

?Features in the same hidden unit will“com-bine”with each other through our tanh-cube activation function.As we can see,feature combination in hidden unit2were also used in Mcdonald and Pereira(2006).However, these feature combinations are automatically captured by our model without the labor-intensive feature engineering.

?Hidden unit3to5show that phrase-level information like hm pre?x,hm suf?x and sm in?x are effective in our model.These features are not used in conventional second-order model(McDonald and Pereira,2006) because they could explode the feature space.

Through our tanh-cube activation function, our model further captures the interactions between phrases and other features without the concern of over?tting.

5Related Work

Models for dependency parsing have been stud-ied with considerable effort in the NLP commu-nity.Among them,we only focus on the graph-based models here.Most previous systems ad-dress this task by using linear statistical models with carefully designed context and structure fea-tures.The types of features available rely on tree factorization and decoding algorithm.Mcdonald et.al(2005)proposed the?rst-order model which is also know as arc-factored model.Ef?cient de-coding can be performed with Eisner(2000)algo-rithm in O(n3)time and O(n2)space.Mcdonald and Pereira(2006)further extend the?rst-order model to second-order model where sibling infor-mation is available during decoding.Eisner(2000)

algorithm can be modi?ed trivially for second-order decoding.Carreras(2007)proposed a more powerful second-order model that can score both sibling and grandchild parts with the cost of O(n4) time and O(n3)space.To exploit more struc-ture information,Koo and Collins(2010)pro-posed three third-order models with computational requirements of O(n4)time and O(n3)space. Recently,neural network models have been in-creasingly focused on for their ability to minimize the effort in feature engineering.Chen et.al(2014) proposed an approach to automatically learning feature embeddings for graph-based dependency parsing.The learned feature embeddings are used as additional features in conventional graph-based model.Le and Zuidema(2014)proprosed an in?nite-order model based on recursive neural net-work.However,their model can only be used as an reranking model since decoding is intractable. Compared with these work,our model is a general and standalone neural network model. Both training and decoding in our model are per-formed based on our neural network architecture in an effective way.Although only?rst-order and second-order models are implemented in our work,higher-order graph-based models can be easily implemented using our model.

6Conclusion

In this paper,we propose a general and effec-tive neural network model that can automatically learn feature combinations with our novel acti-vation function.Moreover,we introduce a sim-ple yet effect way to utilize phrase-level informa-tion,which greatly improves the model perfor-mance.Experiments on the benchmark dataset show that our model achieves better results than conventional models.

Acknowledgments

This work is supported by National Natural Science Foundation of China under Grant No. 61273318and National Key Basic Research Pro-gram of China2014CB340504.We want to thank Miaohong Chen and Pingping Huang for their valuable comments on the initial idea and helping pre-process the data.References

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对等网络模式

一、对等网简介 “对等网”也称“工作组网”,那是因为它不像企业专业网络中那样是通过域来控制的,在对等网中没有“域”,只有“工作组”,这一点要首先清楚。正因如此,我们在后面的具体网络配置中,就没有域的配置,而需配置工作组。很显然,“工作组”的概念远没有“域”那么广,所以对等网所能随的用户数也是非常有限的。在对等网络中,计算机的数量通常不会超过20台,所以对等网络相对比较简单。在对等网络中,对等网上各台计算机的有相同的功能,无主从之分,网上任意节点计算机既可以作为网络服务器,为其它计算机提供资源;也可以作为工作站,以分享其它服务器的资源;任一台计算机均可同时兼作服务器和工作站,也可只作其中之一。同时,对等网除了共享文件之外,还可以共享打印机,对等网上的打印机可被网络上的任一节点使用,如同使用本地打印机一样方便。因为对等网不需要专门的服务器来做网络支持,也不需要其他组件来提高网络的性能,因而对等网络的价格相对要便宜很多。 对等网主要有如下特点: (1)网络用户较少,一般在20台计算机以内,适合人员少,应用网络较多的中小企业; (2)网络用户都处于同一区域中; (3)对于网络来说,网络安全不是最重要的问题。 它的主要优点有:网络成本低、网络配置和维护简单。 它的缺点也相当明显的,主要有:网络性能较低、数据保密性差、文件管理分散、计算机资源占用大。 二、对等网结构 虽然对等网结构比较简单,但根据具体的应用环境和需求,对等网也因其规模和传输介质类型的不同,其实现的方式也有多种,下面分别介绍: 1、两台机的对等网 这种对等网的组建方式比较多,在传输介质方面既可以采用双绞线,也可以使用同轴电缆,还可采用串、并行电缆。所需网络设备只需相应的网线或电缆和网卡,如果采用串、并行电缆还可省去网卡的投资,直接用串、并行电缆连接两台机即可,显然这是一种最廉价的对等网组建方式。这种方式中的“串/并行电缆”俗称“零调制解调器”,所以这种方式也称为“远程通信”领域。但这种采用串、并行电缆连接的网络的传输速率非常低,并且串、并行电缆制作比较麻烦,在网卡如此便宜的今天这种对等网连接方式比较少用。 2、三台机的对等网

(完整版)博客系统需求分析

校园博客系统需求分析 评审日期:2010 年04 月01 日 目录 1导言 (1)

1.2范围 (1) 1.3缩写说明 (1) 1.4术语定义 (1) 1.5引用标准 (1) 1.6参考资料 (2) 2系统定义 (2) 2.1项目来源及背景 (2) 2.2系统整体结构 (2) 3应用环境 (3) 3.1系统运行网络环境 (3) 3.2系统运行硬件环境 (4) 3.3系统运行软件环境 (4) 4功能规格 (4) 4.1角色( A CTOR )定义 (5) 4.1.1博客访问者 (5) 4.1.2管理用户 (5) 4.1.3 数据库 (6) 4.2系统主U SE C ASE图. (6) 4.3客户端子系统 (6) 4.4管理端子系统 (8) 4.4.1 登录管理 ....................................................... 10 4.4.2 类型管理 ......................................................... 11 4.4.3 评论管理 ....................................................... 12 4.4.4 留言管理 ....................................................... 12 4.4.5 图片管理 ....................................................... 12 4.4.6 用户管理 ....................................................... 13 5性能需求 (13) 5.1 界面需求 (13) 5.2响应时间需求 (13) 5.3可靠性需求 (13) 5.4开放性需求 (14) 5.5可扩展性需求 (14) 5.6系统安全性需求 (14) 6产品提交 (14)

个人博客简介

1.1 博客信息系统概述 “博客”(Blog或Weblog)一词源于“Web Log(网络日志)”的缩写,是一种十分简易的傻瓜化个人信息发布方式。任何人都可以像使用免费电子邮件一样,完成个人网页的创建、发布和更新。博客就是开放的私人空间,可以充分利用超文本链接、网络互动、动态更新等特点,在网络中,精选并链接全球互联网中最有价值的信息、知识与资源;也可以将个人工作过程、生活故事、思想历程、闪现的灵感等及时记录和发布,发挥个人无限的表达力;更可以以文会友,结识和汇聚朋友,进行深度交流沟通[1]。 “博客”当然是个大家都陌生的名词,博客的英文名词就是“Blog或Weblog”(指人时对应于Blogger),是一个典型的网络新事物,查阅最新的英文词典也不可能查到。该词来源于“Web Log(网络日志)”的缩写,特指一种特别的网络个人出版形式,内容按照时间顺序排列,并且不断更新。 博客是一种零编辑、零技术、零成本、零形式的网上个人出版方式。 博客概念一般包含了三个要素(当然,也不需要局限这些定义): (1)网页主体内容由不断更新的、个性化的众多日志组成。 (2)按时间顺序排列,而且是倒序方式,也就是最新的放在最上面,最旧的放在最下面。 (3)内容可以是各种主题、各种外观布局和各种写作风格,但是文章内容以“超链接”作为重要的表达方式。 因此,博客是个人性和公共性的结合体,其精髓不是主要表达个人思想,不是主要记录个人日常经历;而是以个人的视角,以整个互联网为视野,精选和记录自己在互联网上看到的精彩内容,为他人提供帮助,使其具有更高的共享价值。 博客精神的核心并不是自娱自乐,甚至不是个人表达自由,相反,是体现一种利他的共享精神,为他人提供帮助。个人日记和个人网站主要表现的还是“小我”,而博客表现的是“大我”。也许形式上很接近,但内在有着本质的差异。所有优秀博客网站中,真正表达作者个人的内容非常有限,最多只是点缀,而不像个人网站那样是核心。 1.2 博客发展趋势 趋势一:博客现在正在形成个人的信誉机制,有了博客之后就确立了一个个人虚拟身份,简单的来讲就是个人在互联网上是有名有姓的,而不再是一种匿名的行为,网民从流浪汉变成了一个定居者。以前在互联网上的各种行为都是在匿名状态中,相互之间是不认识的,但有了博客之后可以天天关注,而别的人也可

日志分析系统

Web日志集中管理系统的研究与实现 吴海燕朱靖君程志锐戚丽 (清华大学计算机与信息管理中心,北京100084) E-mail:wuhy@https://www.wendangku.net/doc/2f10629436.html, 摘要: Web服务是目前互联网的第一大网络服务,Web日志的分析对站点的安全管理与运行维护非常重要。在实际运行中,由于应用部署的分散性和负载均衡策略的使用,使得Web日志被分散在多台服务器上,给日志的管理和分析带来不便。本文设计并实现了一个Web日志集中管理系统(命名为ThuLog),系统包括日志集中、日志存储和日志分析三个模块。目前,该系统已经在清华大学的多个关键Web应用系统上进行了应用,能够帮助系统管理员清晰地了解系统运行情况,取得了较好的运行效果。 关键词:Web日志日志分析日志集中管理系统 The Research and Implementation of a Centralized Web Log Management System Wu Haiyan Zhu Jingjun Cheng Zhirui Qi Li (Computer&Information Center,Tsinghua University,Beijing100084) Abstract:Web is now the biggest network service on the Internet.The analysis of Web logs plays an important role in the security management and the maintenance of a website.But because of the decentralization of deployment and the use of load balancing,Web logs are often seperated on each Web server,which makes the management and analysis of them not so convenient.This paper designs and implements a Web Log Centralized Management System(named ThuLog),which includes3modules:the centralization of logs,the storage of logs and the analysis of logs.Through log analysis of several critical Web systems in Tsinghua University,it could help system administrators learn clearly what happens in information systems and achieves good operating results. Key words:Web Logs Log Analysis Web Log Centralized Management System 1.引言 近年来,随着计算机网络技术的迅速发展,Web正以其广泛性、交互性、快

博客系统需求分析报告

博 客 系 统 需 求 分 析 报 告 院系:信息电子工程学院 班级:软件08-1 设计小组人员:29号 日期:2010年5月24日

一、系统概述 “博客”一词是从英文单词Blog音译(不是翻译)而来。Blog是Weblog 的简称,而Weblog则是由Web和Log两个英文单词组合而成。 Weblog就是在网络上发布和阅读的流水记录,通常称为“网络日志”,简称为“网志”。博客(BLOGGER)概念解释为网络出版(Web Publishing)、发表和张贴(Post-这个字当名词用时就是指张贴的文章)文章,是个急速成长的网络活动,现在甚至出现了一个用来指称这种网络出版和发表文章的专有名词——Weblog,或Blog。 在网络上发表Blog的构想始于1998年,但到了2000年才开始真正流行。而2000年博客开始进入中国,并迅速发展,但都业绩平平。直到2004年木子美事件,才让中国民众了解到了博客,并运用博客。2005年,国内各门户网站,如新浪、搜狐,原不看好博客业务,也加入博客阵营,开始进入博客春秋战国时代。起初,Bloggers将其每天浏览网站的心得和意见记录下来,并予以公开,来给其他人参考和遵循。但随着Blogging快速扩张,它的目的与最初已相去甚远。目前网络上数以千计的Bloggers发表和张贴Blog的目的有很大的差异。不过,由于沟通方式比电子邮件、讨论群组更简单和容易,Blog已成为家庭、公司、部门和团队之间越来越盛行的沟通工具,因为它也逐渐被应用在企业内部网络(Intranet)。目前,国内优秀的中文博客网有:新浪博客,搜狐博客,中国博客网,腾讯博客,博客中国等。 二、需求分析 博客系统是一个多用户、多界面的系统,主要包括以下几个模块组成。 1.匿名用户模块 本模块主要由注册、登录、浏览博客、评论4个部分组成。匿名用户可以对其他用户的博客内容时行浏览、评论。也可以通过注册后登录博客系统,申请一个属于自己的博客。 2.注册用户模块 本模块主要由个人信息管理、评论管理、好友管理、相册管理、文章管理5

对等网络配置及网络资源共享

物联网技术与应用 对等网络配置及网络资源共享 实验报告 组员:

1.实验目的 (1)了解对等网络基本配置中包含的协议,服务和基本参数 (2)了解所在系统网络组件的安装和卸载方法 (3)学习所在系统共享目录的设置和使用方法 (4)学习安装远程打印机的方法 2.实验环境 Window8,局域网 3.实验内容 (1)查看所在机器的主机名称和网络参数,了解网络基本配置中包含的协议,服务和基本参数 (2)网络组件的安装和卸载方法 (3)设置和停止共享目录 (4)安装网络打印机 4.实验步骤 首先建立局域网络,使网络内有两台电脑 (1)“我的电脑”→“属性”,查看主机名,得知两台计算机主机名为“idea-pc”和“迦尴专属”。 打开运行输入cmd,进入窗口输入ipconfig得到相关网络参数。局域网使用的是无线局域网。 (2)网络组件的安装和卸载方法:“网络和共享中心”→“本地连接”→“属

性”即可看到网络组件,可看其描述或卸载。 “控制面板”→“卸载程序”→“启用和关闭windows功能”,找到internet 信息服务,即可启用或关闭网络功能。 (3)设置和停止共享目录(由于windows版本升高,加强了安全措施和各种权

限,所以操作增加很多) 使用电脑“idea-pc”。“打开网络和共享中心”→“更改高级选项设置”。将专用网络,来宾或公用,所有网络中均选择启用文件夹共享选项,最下面的密码保护项选择关闭,以方便实验。 分享文件夹“第一小组实验八”,“右键文件夹属性”→“共享”→“共享”,选择四个中的一个并添加,此处选择everyone,即所有局域网内人均可以共享。

对等网络(P2P)总结整理解析

对等网络(P2P 一、概述 (一定义 对等网络(P2P网络是分布式系统和计算机网络相结合的产物,在应用领域和学术界获得了广泛的重视和成功,被称为“改变Internet的新一代网络技术”。 对等网络(P2P:Peer to Peer。peer指网络结点在: 1行为上是自由的—任意加入、退出,不受其它结点限制,匿名; 2功能上是平等的—不管实际能力的差异; 3连接上是互联的—直接/间接,任两结点可建立逻辑链接,对应物理网上的一条IP路径。 (二P2P网络的优势 1、充分利用网络带宽 P2P不通过服务器进行信息交换,无服务器瓶颈,无单点失效,充分利用网络带宽,如BT下载多个文件,可接近实际最大带宽,HTTP及FTP很少有这样的效果 2、提高网络工作效率 结构化P2P有严格拓扑结构,基于DHT,将网络结点、数据对象高效均匀地映射到覆盖网中,路由效率高 3、开发了每个网络结点的潜力 结点资源是指计算能力及存储容量,个人计算机并非永久联网,是临时性的动态结点,称为“网络边缘结点”。P2P使内容“位于中心”转变为“位于边缘”,计算模式由“服务器集中计算”转变为“分布式协同计算”。

4、具有高可扩展性(scalability 当网络结点总数增加时,可进行可扩展性衡量。P2P网络中,结点间分摊通信开销,无需增加设备,路由跳数增量小。 5、良好的容错性 主要体现在:冗余方法、周期性检测、结点自适应状态维护。 二、第一代混合式P2P网络 (一主要代表 混合式P2P网络,它是C/S和P2P两种模式的混合;有两个主要代表: 1、Napster——P2P网络的先驱 2、BitTorrent——分片优化的新一代混合式P2P网络 (二第一代P2P网络的特点 1、拓扑结构 1混合式(C/S+P2P 2星型拓扑结构,以服务器为核心 2、查询与路由 1用户向服务器发出查询请求,服务器返回文件索引 2用户根据索引与其它用户进行数据传输 3路由跳数为O(1,即常数跳 3、容错性:取决于服务器的故障概率(实际网络中,由于成本原因,可用性较低。

博客系统需求分析报告1

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理和维护。通过系统管理员写入的用户名,密码登录到网站。网站检测用户的用户名,密码并给予其相应的权限对博客网站进行操作。 用户退出:已经登陆的用户可以退出,释放自己所占有的各种信息资源。 (2)文章管理 文章管理主要有文章的发表、查询、浏览、评论和删除功能。 博客的系统管理员除了可以查询、浏览和评论文章外,还可以对系统中的所有文章以及评论进行修改、删除操作。这些维护和管理拥有最高权限,并且系统自动更新在服务器端数据库中的数据。 文章的发表:博客用户可以发表自己的文章,文章包括主题、正文、表情、图片等信息,作者通过各种元素来展示自己的想法和思想。系统接受这些信息并且存储在服务器端的数据库中。 文章的删除:博客用户可以删除自己已经发表的文章内容和各项信息,系统自动在服务器端数据库中删除这些记录。 文章的浏览:游客和博客用户根据所获得的用户权限获取服务器端数据存储的各篇文章并且浏览阅读文章的所有信息,包括标题、正文、表情、图片以及其它读者的留言评论。 文章的评论:文章的读者可以评论和回复所阅读的文章,发表自己的看法。系统自动将这些评论存储在服务器端的数据库中,并且可供博客作者以及其它读者浏览。 文章的查询:博客用户可以按文章题目或作者来查询想要查的文章。 文章中还可能包含一些图片视频等多媒体,所以文章管理中还包含了网站中媒体的管理。 媒体管理有添加,浏览、删除和查询功能。博客用户可以添加自己喜欢的图片或视频等,还可以查询和浏览系统中的所有媒体信息。游客只能浏览博客系统中的媒体信息。系统管理员拥有以上的所有权限,除此之外还可以删除媒体信息。 (3)博客管理员管理 博客管理员可以添加、删除新用户,用户的角色又分为订阅者、作者、编辑、投稿者、管理员。 还可以对博客主页的外观、博客使用的插件、工具进行添加、删除、设置。

博客作用

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对等网络的网络弹性分析

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具有集散节点和集群结构的无标度网络,对意外故障具有极强的承受能力,但面对蓄意的攻击和破坏却不堪一击[2]。在随机网络中,如果大部分节点发生瘫痪,将不可避免地导致网络的分裂。无标度网络的模拟结果则展现了全然不同的情况,随意选择高达80%的节点使之失效,剩余的网络还可能组成一个完整的集群并保持任意两点间的连接,但是只要5%―10%的集散节点同时失效,就可导致互联网溃散成孤立无援的小群路由器。 许多复杂网络系统显示出惊人的容错特性,例如复杂通信网络也常常显示出很强的健壮性,一些关键单元的局部失效很少会导致全局信息传送的损失。但并不是所有的网络都具有这样的容错特性,只有那些异构连接的网络,即无标度网络才有这种特性,这样的网络包括WWW、因特网、社会网络等。虽然无标度网络具有很强的容错性,但是对于那些有意攻击,无标度网络却非常脆弱。容错性和抗攻击性是通信网络的基本属性,可以用这两种属性来概括网络弹性。 对等网络技术和复杂网络理论的进展促使对现有对等 网络的拓扑结构进行深入分析。对网络弹性的认识可以使从网络拓扑的角度了解网络的脆弱点,以及如何设计有效的策略保护、减小攻击带来的危害。本文研究Gnutella网络的网络弹性,并与ER模型和EBA模型进行了比较,对比不同类 型的复杂网络在攻击中的网络弹性。当网络受到攻击达到某

博客需求分析

博客系统需求分

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